Detection of circulating autoantibodies using living keratinocyte staining on MCA-B1 method in dogs with pemphigus foliaceus

In this study, we compared the sensitivity and specificity of three immunofluorescence techniques used to detect circulating autoantibodies in dogs with pemphigus foliaceus (PF); living keratinocyte staining on a canine keratinocyte cell line, MCA-B1, indirect immunofluorescence (IIF) on canine lip and IIF on bovine esophagus. Sera from canine PF cases were positive in four out of 27 dogs (14.8%) using living keratinocyte staining on MCA-B1 cells method, and five (18.5%) and eight sera (29.6%) using IIF on canine lip and bovine esophagus methods, respectively. By contrast, none of the 31 sera from dogs with non-pemphigus dermatoses reacted with MCA-B1 cells, whereas two (6.5%) as well as five sera (16.1%) obtained from those dogs showed positive reactivity with IIF on canine lip and bovine esophagus, respectively. Our results suggest that, although it exhibits the least sensitivity, the positive reactivity obtained by living keratinocyte staining on MCA-B1 cells can support the diagnosis of canine PF.     

Production and preliminary characterization of monoclonal antibodies to chicken anemia agent

Mice were immunized with partially purified preparations of the Cux-1 isolate of chicken anemia agent (CAA), and their splenocytes were fused with NSO myeloma cells. Three patterns of staining of CAA-infected cells were recognized when the resulting hybridomas were screened by indirect immunofluorescence (IIF). Hybridomas representative of each staining pattern were cloned, and the monoclonal antibodies (MAbs) were characterized. Type 1 staining was indistinguishable from that produced by polyclonal chicken antisera to CAA. Type 2 staining was confined to large nuclear inclusions. Type 3 staining was predominantly nuclear and granular, and differed from type 1 in being more intense and occurring in a higher proportion of nuclei. Three MAbs producing type 1 staining were predominantly Cux-1-specific by IIF; they also reacted to lower titers with the Gifu-1 isolate but not at all with three other CAA isolates. These MAbs had very slight neutralizing activity against Cux-1. Another MAb giving type 1 staining reacted with all CAA isolates tested to high titers in IIF and neutralization tests. MAbs with type 2 and type 3 staining reacted by IIF with all CAA isolates tested but possessed no neutralizing activity. The availability of MABs to CAA should facilitate development of diagnostic tests for the virus.     

A peptide vaccine administered transcutaneously together with cholera toxin elicits potent neutralising anti-FMDV antibody responses

In this study a synthetic peptide representing residues 141-159 from the GH loop of VP1 protein of foot-and-mouth disease virus was tested for its capacity to elicit virus neutralising antibodies in mice after transcutaneous immunisation. Topical application of the peptide conjugated to bovine serum albumin together with cholera toxin as an adjuvant elicited anti-peptide antibody responses with strong virus neutralising activity. The combination of cholera toxin with an immunostimulatory CpG motif resulted in the induction of IgG1 and IgG2a anti-peptide antibodies with significantly enhanced virus neutralising activity. To shed more light on the mechanisms of cholera toxin adjuvanticity we demonstrated its binding to keratinocytes via GM(1)-gangliosides. This was followed by an increase of the intracellular cAMP and the rapid diffusion of cholera toxin throughout the epidermis. These findings demonstrate that peptide-based vaccines when combined with the appropriate adjuvant(s) can elicit potent virus neutralising antibody responses after transcutaneous immunisation. However, experiments in target species will be required to confirm the potential of this simple vaccination procedure in livestock.     

Detection of antinuclear antibodies by the Inno‐Lia ANA update test in canine systemic rheumatic disease

Background: Certain systemic autoimmune diseases in dogs are characterized by high titers of circulating antinuclear antibodies (ANA), which can be demonstrated by indirect immunofluorescence (IIF). In an earlier study of IIF‐ANA–positive dogs, the Ouchterlony double immunodiffusion (DID) test was used to identify specific autoantibodies. The DID test has largely been replaced with line blot tests in human diagnostic settings. Objective: The objective of this study was to investigate whether the line blot assay Inno‐Lia ANA update test is a useful tool in demonstrating ANA specificities in canine patients with previously diagnosed IIF‐ANA–positive rheumatic disorders. Methods: Serum samples from 3 clinically healthy control dogs and 20 canine patients with clinical signs of systemic rheumatic disease and documented positive results for IIF‐ANA and DID tests were included in the study. The Inno‐Lia ANA update assay was performed with an anti‐canine detection antibody. Results: Six serum samples that had DID positivity with anti‐spliceosomal small nuclear ribonucleoproteins (snRNP) reactivity showed reactivity to multiple snRNP proteins in the Inno‐Lia test. Samples from 2 dogs that had other types of DID positivity also had clear SmB reactivity and 1 had weak reactivity to RNP‐70K. The other serum samples, including controls, were negative. Conclusions: Using the Inno‐Lia ANA update test, multiple snRNP specificities were demonstrated in some canine patients with autoimmune rheumatic disorders. Other canine autoantibodies may exist that are not detected by this test. Further studies are necessary to characterize the target antigen(s) of these remaining autoantibodies in canine sera.     

Serologic examination of aborted ovine and bovine fetal fluids for the diagnosis of border disease, bluetongue, bovine viral diarrhea, and leptospiral infections

Fetal serum from most of 994 bovine and 553 ovine aborted fetuses was tested serologically for antibodies to border disease (BD), bovine viral diarrhea (BVD), and bluetongue (BT) viruses, and to Leptospira sp., and the results were compared with the results of isolation procedures, fluorescent antibody tests (FAT), and histologic examinations of the same fetuses. Antibodies to BT virus were not found in any of the 994 bovine and 553 ovine fetuses. Antibody titers to BVD virus were present in 39 of 966 bovine fetuses tested, and BVD virus was detected in 4 of the 39. Four of 74 fetuses in which the BVD virus was detected by FAT or isolation had titers to BVD virus. Microagglutination (MAT) titers to 1 or more of 5 serovars of leptospires were present in 52 of 773 bovine fetal sera tested. Leptospires were not detected by FAT in any bovine fetuses that had leptospiral antibody titers. Leptospires were detected by FAT in 15 aborted calves, and none of these had MAT titers. Antibody titers to BD virus were present in 80 of 486 fetal lamb sera tested, and the virus was detected by FAT or isolation in 3 of the 80 fetuses. Border disease virus was detected in 14 of 486 fetal lambs tested. Twelve of the 14 were tested serologically and 3 had titers to BD virus. Leptospiral antibody titers were present in 27 of 326 ovine fetal sera tested. Leptospires were not detected in any of the 326 ovine fetuses tested by FAT.     

Serological titers to bovine herpesvirus 1, bovine viral diarrhea virus, parainfluenza 3 virus, bovine respiratory syncytial virus and Pasteurella haemolytica in feedlot calves with respiratory disease: associations with bacteriological and pulmonary cytological variables.

Acute and convalescent serum samples were taken from 59 calves with signs of respiratory disease (cases) and 60 clinically normal animals (controls) during their first month in the feedlot. Sera were analyzed for antibodies to bovine parainfluenza 3 (PI3) virus by hemagglutination inhibition, to bovine viral diarrhea (BVD) virus, bovine respiratory syncytial (BRS) virus and bovine herpesvirus 1 (BHV1) by virus neutralization, and to Pasteurella haemolytica by indirect agglutination (PhIA) and cytotoxin neutralization (PhCN) tests. There was minimal evidence of serological activity to BHV1. Serological activity to the other agents occurred commonly and the prevalence of acute titers and their mean values was similar in case and control groups. Mean convalescent PI3 and P. haemolytica (PhIA) titers were higher in controls than cases (p < 0.01) but, otherwise, convalescent titers did not differ between groups. The incidence of seroconversion was similar in both groups for all agents except for PI3 virus which was more frequent in controls than cases (p < 0.0001). There was a positive association between PhIA and CN seroconversion and isolation of P. haemolytica from bronchoalveolar lavage (BAL) fluid (p < 0.1). The measure of agreement (kappa) between seroconversion with the P. haemolytica PhIA and PhCN tests was 0.51. Bacteriological and cytological evaluations of the respiratory tract were made using BAL. No associations were evident between serological titers and pulmonary cytology. A multivariate logistic analysis was used to evaluate associations between disease status and serological, bacteriological and cytological data. Cases were positively associated with the presence of neutrophils and Pasteurella multocida in BAL fluid and negatively associated with PI3 virus and PhIA seroconversion.     

Maternal immunity to infectious bovine rhinotracheitis and bovine viral diarrhea viruses: duration and effect on vaccination in young calves.

The immune response to modified live-virus bovine viral diarrhea (BVD) vaccine and infectious bovine rhinotracheitis (IBR) vaccine was examined in calves that had received passive maternal antibodies to these viruses. Blood serum samples from vaccinated and control (nonvaccinated) calves were examined for more than 1 year to determine the rate of decline of passive anti-BVD and anti-IBR antibodies and the effect that vaccination had on these antibody titers. The control calves lost their antibodies to BVD and IBR viruses at the rate of one half their remaining antibody titer every 21 days. Calves serologically responded to BVD vaccine at a time when maternal antibody titers remained between 1:96 and 1:20. However, animals did not seroconvert to the IBR vaccine until maternal antibodies had decreased and become undetectable. Evidence is presented to show that although passive immunity will inhibit IBR vaccination, priming for a secondary response will occur so that on subsequent vaccination, at a time when maternal antibodies have disappeared, the animals will respond anamnestically to IBR vaccination.     

Investigations on the nature and pathogenicity of circulating antikeratinocyte antibodies in dogs with pemphigus foliaceus

In humans with pemphigus foliaceus (PF), pathogenic autoantibodies are principally of IgG4 subclass and they cause superficial vesiculation when injected into neonatal mice. The objectives of this study were to determine the isotypes of circulating antikeratinocyte antibodies in dogs with PF, to assess whether serum antikeratinocyte antibody titres decreased during successful treatment, and to study whether such antibodies were pathogenic in passive transfers. Using indirect immunofluorescence with neonatal mouse skin substrates, circulating antikeratinocyte IgG antibodies were detected in 36 of 44 dogs with PF (82%). Serum autoantibodies belonged predominantly to IgG4 (three of 44; 80%) and IgG1 (30 of 44; 68%) subclasses. Antikeratinocyte IgG antibodies were detected in 16 of 20 normal dogs (80%), and these antibodies were IgG1 (16 of 20, 80%) but rarely IgG4 (two of 20; 10%) isotypes. In four dogs, IgG4 antikeratinocyte antibody titres decreased concomitantly to lesions nearing or reaching complete remission. In contrast, IgG or IgG1 titres remained stable or increased when lesions abated. Antikeratinocyte antibodies targeted mainly intercellular autoantigen(s) in the stratum granulosum, while in fewer dogs, such antibodies bound to cytoplasmic basal antigen(s). Intradermal injections of PF or pemphigus vulgaris (PV) IgG into neonatal mice caused subgranular or suprabasal acantholytic vesiculation without granulocyte infiltration, respectively. Similar transfers of normal dog IgG did not cause vesiculation. These observations suggest that antikeratinocyte IgG4 antibodies could be relevant to disease pathogenesis. Importantly, canine PF or PV IgG appear to be pathogenic when transferred passively into mice, causing vesiculation at epidermal levels similar to those of the natural disease.     

The frequency, distribution and effects of antibodies, to seven putative respiratory pathogens, on respiratory disease and weight gain in feedlot calves in Ontario.

During 1983-85, 279 calves requiring treatment for bovine respiratory disease and 290 comparison (control) animals from 15 different groups of feedlot calves were bled on arrival and again at 28 days postarrival. Their sera were then analyzed for antibodies to seven putative respiratory pathogens. On arrival, the prevalences of indirect agglutination titers to Pasteurella haemolytica, P. haemolytica cytotoxin, Mycoplasma bovis and M. dispar were greater than 50%, the prevalence of titers to bovine virus diarrhea virus (BVDV) was approximately 40%, and the prevalences of titers to infectious bovine rhinotracheitis virus (IBRV), bovine respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV3) were all below 25%. Seroconversion during the first month after arrival occurred in more than half the calves to P. haemolytica cytotoxin, PIV3 and RSV. Seroconversion of agglutination titers to P. haemolytica, Mycoplasma and BVDV occurred in about 40% of calves, and seroconversion to IBRV was infrequent (less than 5%). Initial titers were negatively correlated to subsequent titer changes within organism. Initial titers, and titer changes between organisms were essentially independent. Light calves had an increased risk of being selected for treatment for respiratory disease. Seroconversion to P. haemolytica cytotoxin, RSV and BVDV were predictive of respiratory disease cases, explaining approximately 69% of all respiratory disease cases in the feedlots. It was not possible to accurately predict weight gain or relapse from the serological data.     

Systemic lupus erythematosus in a colony of dogs

A colony of dogs was obtained by the mating of a female German Shepherd Dog crossbred and a male Belgian Shepherd Dog crossbred, both with systemic lupus erythematosus (SLE). The colony also contained 16 dogs representing F1, F2, and F3 generations. Ten colony dogs had circulating antinuclear antibodies, and 5 of the 10 had clinical signs of SLE. Two F3-generation females had signs of severe SLE. Two dogs had antibodies to extractable nuclear antigen, notably 1 dog had antibodies to Smith (Sm) antigen and 1 had antibodies to Sjogren syndrome A (SSA) antigen. Thymulin (serum thymic factor associated with zinc) titers were generally low in the descendants, but fluctuations were detected within the same dog. In vitro response of lymphocytes from these colony dogs to concanavalin A was maximal for lower mitogenic concentrations, compared with response of lymphocytes from 10 healthy dogs. The suppressive lymphocyte activity in 6 autoimmune colony dogs was diminished in comparison with the activity in 5 nonautoimmune colony dogs and 6 healthy dogs.     

Neutrophils contact to plasma membrane of keratinocytes including desmosomal structures in canine pemphigus foliaceus

Pemphigus foliaceus (PF) is an autoimmune blistering skin disease that affects certain mammals including dogs. In canine PF, neutrophils are infiltrated intensely into pustular lesions including acantholytic cells, although neutrophilic infiltration is not characterized in human PF. The roles of the neutrophils in the cutaneous lesions of canine PF have not yet been understood. The purpose of this study was to characterize the ultrastructural features underlying the acantholysis with pustule formation in canine PF. Four dogs diagnosed as PF on the basis of clinical signs, histopathological findings, and direct and indirect immunofluorescence examinations were performed. Electron microscopy revealed that the acantholytic cells were adjacent to multiple neutrophils in the pustules. At the contact points between neutrophils and acantholytic keratinocytes, half-desmosomes of acantholytic keratinocytes with intact attachment plaques were observed within invaginations of neutrophils. Furthermore, on the surface of acantholytic cells in the pustules, neutrophil granules seemed to be secreted to the surface of acantholytic cells and to degenerate the half-desmosome structures. Neutrophils were also observed within the epidermis adjacent to the pustule. At the intercellular gap between two dissociated keratinocytes, neutrophils inserted its pseudopodia into the gap between the two half-desmosomes of keratinocytes. These findings taken together suggested that, at least in the areas where we analyzed ultrastructurally, neutrophils contact desmosomal structures and seem to play some parts in separation of keratinocytes and degeneration of split-desmosomes in pustules of dogs with PF.     

Effect of passive immunity on the development of a protective immune response against bovine viral diarrhea virus in calves

OBJECTIVE: To determine whether passively acquired antibodies prevent development of a protective immune response to live virus in calves. ANIMALS: 18 calves. PROCEDURES: Calves were caught immediately after birth and tested free of bovine viral diarrhea virus (BVDV) and serum antibodies against BVDV. Within 48 hours, 12 calves were fed colostrum that contained antibodies against BVDV and 6 calves received BVDV antibody free milk replacer. Three milk replacer fed and 6 colostrum fed calves were exposed to virulent BVDV2-1373 at 2 to 5 weeks of life when passively acquired serum antibody titers were high. After serum antibody titers against BVDV had decayed to undetectable concentrations (at 7 to 9 months of age), the 3 remaining milk replacer fed calves, 6 colostrum fed calves previously exposed to BVDV2-1373, and 6 colostrum fed calves that had not been exposed to the virus were inoculated with BVDV2-1373. RESULTS: Passively acquired antibodies prevented clinical disease in inoculated colostrum fed calves at 2 to 5 weeks of life. Serum antibody titers did not increase in these calves following virus inoculation, and serum antibody titers decayed at the same rate as in noninoculated colostrum fed calves. Inoculated colostrum fed calves were still protected from clinical disease after serum antibody titers had decayed to nondetectable concentrations. Same age colostrum fed calves that had not been previously exposed to the virus were not protected. CONCLUSIONS AND CLINICAL RELEVANCE: A protective immune response was mounted in calves with passive immunity, but was not reflected by serum antibodies titers. This finding has implications for evaluating vaccine efficacy and immune status.     

Hemagglutination and hemagglutination inhibition with Chuzan virus.

Chuzan virus agglutinated erythrocytes of several species of animals including bovine. The hemagglutinating (HA) activity against bovine erythrocytes was dependent on NaCl molarity and was expressed best at 0.6 M, but it was independent of pH and temperature. Three strains of Chuzan virus isolated from 2 cows and a pool of culicoides midges had indistinguishable HA antigenicity. All cattle infected with the virus developed high titers of hemagglutination inhibiting (HI) antibody which changed in parallel with neutralizing (NT) antibody titers. Correlation between HI and NT antibodies was very high and the antibodies persisted for one year or more. Therefore it was concluded that the HI test is applicable for survey of Chuzan virus infection among cattle in place of the NT test.     

Duration of active and colostrum-derived passive antibodies to bovine viral diarrhea virus in calves.

Duration of active and colostrum-derived passive antibodies to bovine viral diarrhea virus was studied in 14 calves. Five calves born with actively induced antibodies to bovine viral diarrhea virus retained high titers during the year of observation. Colostrum-derived antibodies to bovine viral diarrhea virus in nine calves declined at an expected rate for the first four to six months of age. However, titers of six of these calves increased at five to eight months of age and either remained constant or increased through one year of age. Bovine viral diarrhea virus antibody titers of the other three calves declined at a constant rate to less than 1:4 by nine to 12 months of age.     

Detection of Antinuclear Antibodies by Indirect Immunofluorescence in Dog Sera: Comparison of Rat Liver Tissue and Human Epithelial-2 Cells as Antigenic Substrate

Rat liver sections and a human epithelial cell line (HEp-2) were compared as substrates for the detection of antinuclear antibodies (ANA) in the serum of normal dogs and dogs with suspected autoimmune disease, using a standard indirect immunofluorescence (IIF) technique. Antibody reactivity against rat hepatocyte nuclei was frequently found at low serum dilutions in normal dog sera. Using rat liver sections, a minimum significant positive titer, allowing negativity in more than 95% of normal dog sera, was found to be 1/100. With this titer, ANA positivity could be verified in 64 of 112 (57%) reanalysed serum samples from dogs with suspected autoimmune disease, earlier determined as ANA-positive. No reactivity against nuclei of HEp-2 cells was observed in any of the normal dog sera analyzed at a screening dilution of 1/25. Using this dilution as a minimum significant positive titer, 63 of the 112 (56%) re-evaluated serum samples were positive. These 63 samples were from the same dogs as the 64 samples that were positive on rat liver sections. Thus, the 2 methods of ANA-IIF detected a nearly identical population of dogs with suspected autoimmune disease once the level of significance of a positive titer was adjusted to 195% specificity for each method. HEp-2 cells were found to be superior to rat liver cryostate sections as ANA substrate because of their low reactivity with normal sera, and the ease of discernment of the ANA fluorescence pattern. The recognition and documentation of specific pattern types may give clues to ANA subspecificities, which could prove useful if they are found to correlate with well-defined subgroups of immune mediated clinical diseases in dogs. J Vet Intern Med 1996;10:199–203. Copyright © 1996 by the American College of Veterinary Internal Medicine .     

The development of antibodies in rabbits and cattle infected experimentally with an african strain of malignant catarrhal fever virus

An indirect immunofluorescence (IIF) test for antibody to wildebeest-derived strains of malignant catarrhal fever virus (MCFV) was developed using infected bovine embryonic kidney cells as antigen. This IIF technique and a microtitre method for the assay of virus-neutralizing (VN) antibody were then applied to sequential serum samples from rabbits and calves infected experimentally with a virulent strain of MCFV, which caused lethal disease.Antibody of the IIF type appeared in both species about 6–7 days prior to the onset of pyrexia and increased continuously until death. Neutralizing antibody was detected shortly before the end of the incubation period in the majority of rabbits but was not produced in calves which were killed up to 3 days after reaction. The presence of either antibody did not affect the fatal outcome in rabbits.     

Bovine coronavirus (BCV) infections in transported commingled beef cattle and sole-source ranch calves

This study investigated bovine coronavirus (BCV) in both beef calves direct from the ranch and commingled, mixed-source calves obtained from an auction market. The level of BCV-neutralizing antibodies found in the calves varied among ranches in 2 different studies in a retained-ownership program (ROP), from the ranch to the feedlot. Calves with low levels of BCV-neutralizing antibodies (16 or less) were more likely to be treated for bovine respiratory disease (BRD) than those with higher titers. In 3 studies of commingled, mixed-source calves, BCV was recovered from calves at entry to the feedlot and the infections were cleared by day 8. The BCV was identified in lung samples [bronchoalveolar lavage (BAL) collection] as well as in nasal swabs. Calves with low levels of BCV-neutralizing antibodies at entry were most likely to be shedding BCV. Bovine coronavirus was isolated from both healthy and sick calves, but not from sick calves after 4 d arrival at the feedlot. Bovine coronavirus (BCV) should be considered along with other bovine respiratory viruses in the diagnosis of etiologies in bovine respiratory disease, especially for animals that become sick shortly after arrival. If approved vaccines are developed, it would be best to carry out vaccination programs before calves are weaned, giving them sufficient time to gain active immunity before commingling with other cattle.     

Aujeszky's disease ELISA: cross-reactions with other herpesvirus antisera

The production of antibodies in pigs to 11 herpesviruses was investigated in relation to their ability to cross-react with Aujeszky's disease virus (suid herpesvirus 1--SHV1). Of the herpesviruses tested only two, sheep herpesvirus (caprine herpesvirus 1) and dog herpesvirus (canid herpesvirus 1), failed to produce homologous virus antibodies. Only the antibodies to bovine herpesvirus 1 (BHV1) produced a cross-reaction by SHV1 enzyme-linked immunosorbent assay (ELISA). No SHV1 neutralizing antibodies were detected in any of the herpesvirus antisera. A cross-reaction with SHV1 by a serum from a pig naturally infected with BHV1 or with any of the other herpesviruses tested was considered unlikely.     

Borreliosis in dogs from southern Connecticut

Blood samples were obtained from dogs in tick-infested regions of southern Connecticut to assess canine exposure to Borrelia burgdorferi, the etiologic agent of Lyme disease in human beings. An indirect fluorescent antibody test detected immunoglobulin (Ig)M antibodies at titers of 1:64 to 1:512 in 22 of 84 serum samples previously shown to be positive with a polyvalent rabbit anti-dog total Ig conjugate. Analyses of paired serum samples from 20 seropositive dogs revealed temporal differences in titers; changes occurred during brief (1 month) or extended (greater than 4 years) sampling periods. Clinical records for 52 seropositive dogs indicated a history of intermittent lameness in 19 of these. Limb/joint disorders typically developed in dogs without IgM antibodies, suggesting manifestation during later phases of illness. A microscopic-agglutination test was used to assess cross reactivity between B burgdorferi and 20 serovars of Leptospira interrogans and biflexa. Analyses of 63 dog serum specimens with antibodies to B burgdorferi and a series of reference rabbit sera revealed minor antigenic relatedness. There was geographic clustering of dogs with antibodies to B burgdorferi in areas of south-central and southeastern Connecticut, where human Lyme disease also occurs.     

Immunoglobulin M-specific enzyme-linked immunosorbent assay for serodiagnosis of bovine respiratory syncytial virus infections

An antibody-capture enzyme-linked immunosorbent assay (ELISA) for detection of immunoglobulin (Ig) M antibodies to bovine respiratory syncytial virus (BRSV) in cattle was developed. Monoclonal antibody to bovine IgM was used as the catching antibody. The IgM-ELISA was used, as well as a BRSV-specific IgG ELISA to determine the kinetics of IgM and IgG antibody responses to BRSV infections in cattle. High IgM and IgG antibody titers developed after naturally occurring or induced BRSV infection of calves (6 to 7 months old). Induced infection resulted in an IgM response that was first detectable at postinoculation day (PID) 11 reached a maximum at PID 13, and became undetectable again about PID 28. An IgG response also was detected by PID 11. However, a maximum response was not reached before PID 23, and titers remained high (until PID 80). In naturally occurring infection, IgM and IgG responses in calves were observed in the acute phase of epizootics of respiratory tract disease. Patterns of IgM and IgG response curves were similar to those observed in experimentally infected calves. The involvement of BRSV in an epizootic of respiratory tract disease in 8 calves (2 to 3 weeks old) was demonstrated by the detection of BRSV in several lung lavage samples. All calves had existing IgG antibodies to BRSV which were interpreted to be maternally derived. None of the calves responded with an increase in IgG antibody titer. However, a weak but distinct BRSV IgM antibody response occurred in 6 calves.(ABSTRACT TRUNCATED AT 250 WORDS)