CD11b of Ovis canadensis and Ovis aries: molecular cloning and characterization

Leukotoxin (Lkt) is the primary virulence factor secreted by Mannheimia haemolytica which causes pneumonia in ruminants. Previously, we have shown that CD18, the beta subunit of beta(2) integrins, mediates Lkt-induced cytolysis of ruminant leukocytes. CD18 associates with four distinct alpha subunits giving rise to four beta(2) integrins, CD11a/CD18 (LFA-1), CD11b/CD18 (Mac-1), CD11c/CD18 (CR4), and CD11d/CD18. It is not known whether all the beta(2) integrins serve as a receptor for Lkt. Since PMNs are the leukocyte subset that is most susceptible to Lkt, and Mac-1 expression on PMNs exceeds that of other beta(2) integrins, it is of interest to determine whether Mac-1 serves as a receptor for Lkt which necessitates the cloning of CD11b and CD18. In this study, we cloned and sequenced the cDNA encoding CD11b of Ovis canadensis (bighorn sheep) and Ovis aries (domestic sheep). CD11b cDNA is 3455 nucleotides long encoding a polypeptide of 1152 amino acids. CD11b polypeptides from these two species exhibit 99% identity with each other, and 92% with that of cattle, and 70-80% with that of the non-ruminants analyzed.     

Immune evasion by pathogens of bovine respiratory disease complex

Bovine respiratory tract disease is a multi-factorial disease complex involving several viruses and bacteria. Viruses that play prominent roles in causing the bovine respiratory disease complex include bovine herpesvirus-1, bovine respiratory syncytial virus, bovine viral diarrhea virus and parinfluenza-3 virus. Bacteria that play prominent roles in this disease complex are Mannheimia haemolytica and Mycoplasma bovis. Other bacteria that infect the bovine respiratory tract of cattle are Histophilus (Haemophilus) somni and Pasteurella multocida. Frequently, severe respiratory tract disease in cattle is associated with concurrent infections of these pathogens. Like other pathogens, the viral and bacterial pathogens of this disease complex have co-evolved with their hosts over millions of years. As much as the hosts have diversified and fine-tuned the components of their immune system, the pathogens have also evolved diverse and sophisticated strategies to evade the host immune responses. These pathogens have developed intricate mechanisms to thwart both the innate and adaptive arms of the immune responses of their hosts. This review presents an overview of the strategies by which the pathogens suppress host immune responses, as well as the strategies by which the pathogens modify themselves or their locations in the host to evade host immune responses. These immune evasion strategies likely contribute to the failure of currently-available vaccines to provide complete protection to cattle against these pathogens.     

Nerve insensitivity resistance to pyrethroids in Heliothine Lepidoptera

A neurophysiological assay developed previously was used to assess the incidence of nerve insensitivity resistance to synthetic pyrethroids in field strains of Helicoverpa armigera. Almost 70% of individuals from a sample of a highly pyrethroid-resistant population from Jiangsu Province, China were nerve-insensitive. Subsequent selection resulted in a strain homogeneous for expression of this mechanism. Likewise, over 95% of a sample from a strain of the insects from Andhra Pradesh, India were nerve-insensitive and a homogeneous strain was developed. Development of a nerve-insensitive laboratory strain of Heliothis virescens was undertaken but homozygosity could not be obtained. It is suggested that high fitness costs may be associated with this mechanism. The incidence of nerve insensitivity in Heliothine pests is reviewed and the role of phenotypic expression assays in molecular studies highlighted. ©1997 SCI     

Persistence and frequency of application of an insecticide in relation to the rate of evolution of resistance

In an earlier paper, it was demonstrated that in order to delay the evolution of resistance, it is important to ensure that heterozygous carriers of resistance genes are killed so that the R gene is made effectively recessive. How this may be achieved is considered here, with (a) a persistent insecticide declining in effectiveness with time, and (b) a non-persistent insecticide (or fumigant). The relationship between the time taken for the dosage to decline to one-tenth (NGI) and the interval between insecticide applications (N12) was investigated. The optimal value of N12 was found to depend not only on the rate of decline but also on the shape of the degradation curve. Other important factors were (a) the dosage of insecticide applied (the initial effective dominance); (b) the initial frequency of the R gene; (c) the proportion of insects per generation that escaped exposure; and (d) whether selection occurred before or after mating. When considering non-persistent insecticides, it was necessary to distinguish between the short-lived deposit and the space spray, the latter being much less likely to lead to resistance.     

Identification of antifungal compounds from the seed oil ofAzadirachta Indica

Evaluation of the activity of the cold expeller neem oil(Azadirachta indica A. Juss.) and the fractions derived through solvent partitioning, againstDrechslera oryzae, Fusarium oxysporum andAlternaria tenuis showed that the active antifungal fraction is a mixture of tetranortriterpenoids. Further, testing the triterpenoidal mixture derived from the 90% methanol (MeOH) extract of neem oil against 13 phytopathogenic fungi revealed that various species were inhibited to different degrees. Direct preparative High Performance Liquid Chromatography (HPLC) of the active fractions and subsequent bioassay of the semi-pure fractions indicated that the active fractions contained major compounds such as 6-deacetylnimbin, azadiradione, nimbin, salannin and epoxyazadiradione. Pure azadiradione, nimbin, salannin and epoxy-azadiradione did not have appreciable activity. However, when these terpenoids were mixed and bioassayed, they showed antifungal activity, indicating possible additive/synergistic effects.     

Distribution and characterization of IL-10-secreting cells in lymphoid tissues of PCV2-infected pigs

Distribution and characterization of interlukin-10 (IL-10)-secreting cells in lymphoid tissues of pigs naturally infected with porcine circovirus type 2 (PCV2) were evaluated in accordance with PCV2 antigen detection. After screening a total of 56 pigs showing the symptoms of postweaning multisystemic wasting syndrome (PMWS), 15 pigs were PCV2 positive and 5 pigs, which showed stronger positive signals over multiples tissues were further investigated. This study showed that in PCV2-infected lymphoid tissues, particularly mandibular lymph node, spleen and tonsil, IL-10 expression was mainly localized in T-cell rich areas but rarely in B cell rich areas. IL-10 was highly expressed in bystander cells but rarely in PCV2-infected cells. Elevated IL-10 expression was predominantly associated with T cells, but rarely with B cells or with macrophages. The results of this study provide evidence for the role of IL-10 in chronic PCV2 infection and its relation to PCV2 antigen in affected tissues. Constantly elevated levels of IL-10 lead to immunosuppression in persistent and chronic viral infections. The increased IL-10 expression observed in PCV2 infection in this study suggests that IL-10-mediated immunosuppression may play an important role in the pathogenesis and maintenance of naturally occurring PCV2 infection.     

Host-delivered RNAi-mediated root-knot nematode resistance in <Emphasis Type="Italic">Arabidopsis</Emphasis> by targeting <Emphasis Type="Italic">splicing factor</Emphasis> and <Emphasis Type="Italic">integrase</Emphasis> genes

Root-knot nematodes (RKNs) are one of the most important biotic factors limiting crop productivity in many crop plants. The major RKN control strategies include development of resistant cultivars, application of nematicides and crop rotation, but each has its own limitations. In recent years, RNA interference (RNAi) has become a powerful approach for developing nematode resistance. The two housekeeping genes, splicing factor and integrase, of Meloidogyne incognita were targeted for engineering nematode resistance using a host-delivered RNAi (HD-RNAi) approach. Splicing factor and integrase genes are essential for nematode development as they are involved in RNA metabolism. Stable homozygous transgenic Arabidopsis lines expressing dsRNA for both genes were generated. In RNAi lines of splicing factor gene, the number of galls, females and egg masses was reduced by 71.4, 74.5 and 86.6%, respectively, as compared with the empty vector controls. Similarly, in RNAi lines of the integrase gene, the number of galls, females and egg masses was reduced up to 59.5, 66.8 and 63.4%, respectively, compared with the empty vector controls. Expression analysis revealed a reduction in mRNA abundance of both targeted genes in female nematodes feeding on transgenic plants expressing dsRNA constructs. The silencing of housekeeping genes in the nematodes through HD-RNAi significantly reduced root-knot nematode infectivity and suggests that they will be useful in developing RKN resistance in crop plants.     

Vaccination of ducks with recombinant outer membrane protein (OmpA) and a 41 kDa partial protein (P45N') of Riemerella anatipestifer.

The generation of protective immunity against Riemerella anatipestifer infection in ducks were investigated by immunizations with recombinant glutathione sulfatransferase (GST) fusion's proteins of OmpA, a 42kDa major outer membrane protein, and P45N', a 41kDa N-terminal fragment of a newly identified 45kDa potential surface protein from R. anatipestifer. The DNA encoding OmpA and P45N' were isolated from R. anatipestifer serotype 15 (field strain 110/89) and serotype 19 (reference strain 30/90), respectively. Immunoblotting and ELISA results showed that the purified recombinant proteins induced the production of antibodies in immunized ducks. However, neither was protective against subsequent challenge with the virulent serotype 15 strain, 34/90. All the five ducks immunized with formalinized R. anatipestifer strain 34/90 survived the challenge with the homologous strain whereas six out of seven ducks in the non-immunized control group died within a week following the challenge.