The cellular differentiation of M cells from crypt undifferentiated epithelial cells into microvillous epithelial cells in follicle-associated epithelia of chicken cecal tonsils

To clarify the cellular origin and the fate of M cells, detailed distributions of the epithelial cells were investigated scanning electron microscopically on the follicle-associated epithelia (FAE) of chicken cecal tonsils. The distribution of M cells was closely related with the situation of the crypt orifices in chicken cecal tonsils. In undeveloped cecal tonsils, the intestinal crypts were localized at the periphery of the FAE. In these tonsils, M cells without microvilli (M(0)) were predominantly populated in the basal region of the FAE, whereas goblet cells and microvillous epithelial cells (MV) were more distributed in the middle to the apical region of the FAE. A few M cells with short microvilli were dispersed throughout the FAE. Significantly shrunk MV (MVs) clustered together in transitional portions from the lateral face to the roof of the FAE. In well-developed cecal tonsils, the crypts also opened at the lateral surface in addition to the periphery of the FAE. In these tonsils, the M(0) accumulated densely in the small areas around the crypt orifices exclusively. No sign of exfoliation of apoptotic epithelial cells was found in the M(0)-accumulated areas and at their peripheral boundaries. The MVs were often clustered in the central regions among the crypt orifices in addition to the roof of the FAE. These findings suggest that M cells are directly derived from the undifferentiated crypt epithelial cells, not fall into apoptotic cell death and further differentiate into MV in the FAE of chicken cecal tonsils.     

Immunohistochemical study on the delayed progression of epithelial apoptosis in follicle-associated epithelium of rat Peyer's patch

It is well known that some caspases in apoptosis is involved in determinant of terminal differentiation and maturation of various cells. Our previous study ultrastructurally clarified the differentiation into M cells from immature microvillous epithelial cells and the redifferentiation from M cells to microvillous epithelial cells in the follicle-associated epithelium (FAE) of rat Peyer's patch. In this study, the difference of epithelial apoptosis between the FAE of Peyer's patch and intestinal villi was immunohistochemically investigated in rat jejunoileum. As a result, cleaved caspase-3 was limited to several epithelial cells at the tip of FAE, whereas almost all of the epithelial cells were cleaved caspase-3 positive in intestinal villi. Cleaved caspase-9 was detected only in a few exfoliating or exfoliated epithelial cells of both FAE and intestinal villi. Nuclear DNA-fragmentation was detected only in several epithelial cells of the tip of FAE, while it was expressed from the middle regions in the intestinal villi. The DNase I expression of the epithelial cytoplasm was much weaker in FAE than in intestinal villi. Bcl-x expression was restricted in the apical cytoplasms of epithelial cells in the FAE, whereas it was restricted in whole cytoplasms in villous epithelial cells. These findings suggest that the progression of the apoptotic process in the epithelial cells of FAE is later than in the intestinal villi, so that the possibility of epithelial differentiation might be remained in the FAE, unlike in the intestinal villi.     

Distribution of the pores of epithelial basement membrane in the rat small intestine

The distribution and diameter of the pores of epithelial basement membrane in the intestinal villi and the lymph nodules of ileal Peyer's patches were investigated in the rat small intestine by scanning electron microscopy after the removal of the overlying epithelial cells with OsO(4) maceration. In the duodenum, jejunum and ileum, the pores were mainly distributed at the upper three fourths of the villi, but were scarce around the top of the villi. The diameter of some of the pores in the upper three fourths of the villi was larger than that of those in the lower portion. The protrusion of lymphocytes and the cytoplasmic processes of macrophages were also seen at the orifices of the pores. In ileal Peyer's patches, in contrast, pores were densely distributed in the lower one third of the follicle-associated epithelium (FAE) where M cells were mainly seen. Furthermore, these pores were larger than those found in the upper two thirds. Lymphocytes or cytoplasmic processes of macrophages were frequently seen in the lower one third of FAE. These results suggest that the pores at the basement membrane correspond to the passage of the immunocompetent cells which are in contact with M cells or villous columnar epithelial cells and that the abundance of pores is a sign of aggressive interaction between the particular epithelial cells and the immunocompetent cells at the upper three fourths of intestinal villi and the lower one third of FAE in the rat small intestine.     

Cellular kinetics of villous epithelial cells and m cells in rabbit small intestine

The cellular kinetics of villous columnar epithelial cells and M cells in the rabbit small intestine were determined by the use of 5-bromo-2'-deoxyuridine (BrdU) as a tracer. To identify M cells, vimentin antibody was used. The BrdU-labeled nuclei of columnar epithelial cells reached the base of intestinal villi in all portions at 1 day after BrdU administration. Thereafter, BrdU-labeled cells migrated toward the villous tip, but they did not move at a uniform speed. The epithelial cells which existed in intestinal villi on circular folds moved faster than those on mucosa other than circular folds. At 7 days after BrdU administration, the leading edge of BrdU-labeled epithelial cells already disappeared from the villous tip in all portions of the small intestine. In the ileal Peyer's patch, the BrdU-labeled nuclei of microvillous epithelial cells and vimentin-positive M cells appeared near the intestinal crypt orifice at 1 day after BrdU administration, and then migrated toward the luminal surface of the follicle-associated epithelium (FAE). As they moved toward the upper portion of FAE, the number of BrdU-labeled M cells on the side of the dome decreased simultaneously. The leading edge of BrdU-labeled epithelial cells disappeared from the top of the FAE within 7 days. These results suggest that M cells may differentiate from the undifferentiated cells in intestinal crypts within 1 day and disappear from the top of the FAE after the change of their form from M cells into microvillous epithelial cells.     

Special sugar expression on apoptotic epithelial cells of Peyer's patches and intestinal villi in rat small intestine

Our previous study clarified that the apical regions of both the follicle-associated epithelium (FAE) of Peyer's patches and the intestinal villi are the only adhesion sites of indigenous bacteria in rat jejuno-ileum. To survey the ligands against bacterial lectins, sugar expression patterns on epithelial cells were lectin-histochemically investigated using 21 lectins in the jejuno-ileal Peyer's patches of rats. As a result, (D-glcNAc)(2-4), detected by Solanum tuberosum (STL) and by Lycopersicon esculentum (LEL), and beta-D-gal(1-3)-D-galNAc detected by Peanut agglutinin (PNA), were strongly expressed on the brush borders of the apical regions of the FAE and the intestinal villi. On the other hand, neither sugar was expressed on the brush borders of the basal regions of both FAE and intestinal villi. The positive intensities for the lectins correlated with the progression of epithelial apoptosis in the FAE and in the intestinal villi. Moreover, the double staining with lectin histochemical method and the in situ nick end-labeling method could simultaneously detect the strong expression of both sugars and nuclear DNA fragmentation in epithelial cells at the late apoptotic stage. Other sugar expression patterns in the intestinal villi were similar with those in the FAE. There were no lectins specific for M cells in the FAE. From these findings, the possible sugars of ligands against some indigenous bacterial lectins, expressing specially on the apoptotic epithelial cells, might be narrowed down in rat jejuno-ileum.     

鸡十二指肠中T淋巴细胞及其亚群发育的研究

通过免疫组织化学法,应用CD3、CD4和CD8单克隆抗体研究了CD3+T淋巴细胞及CD4+和CD8+T淋巴细胞亚群在鸡盲肠扁桃体中的出现、迁移、组织定位分布及数量变化规律等一系列发育过程。结果显示:CD3+、CD8+T淋巴细胞最初于11胚龄时出现,而CD4+T淋巴细胞在15胚龄时出现。在定位分布变化上,CD3+主要分布在黏膜上皮中,CD4+主要分布在黏膜固有层中,CD8+在黏膜固有层和黏膜上皮内都有大量分布。在数量变化上,1～7日龄雏鸡各种阳性细胞的数量都骤然增加;而到7日龄时,雏鸡CD3+淋巴细胞的数量明显减少,CD4+、CD8+T细胞的数量无明显变化;从21日龄开始直到35日龄,雏鸡CD3+、CD4+和CD8+T淋巴细胞的数量持续增加。试验证明,鸡在出壳后初期十二指肠的细胞免疫功能增强。     

Distribution and developmental change of lymphoid tissues in the chicken proventriculus

In the chicken proventricular mucosa, aggregations of lymphocytes were localized in three different sites of the lamina propria, namely, underneath the surface epithelium, near the duct orifice of the deep proventricular gland, and in the gland tissue itself. In the lymphoid masses underneath the surface epithelium and in those near the duct orifice, CD4+ T lymphocytes and TCR2+ T lymphocytes occupied their central part, and B lymphocytes were localized in the periphery. CD8+ T lymphocytes and TCR1+ lymphocytes were evenly distributed in the masses. Infiltration of lymphocytes into these sites was first observed on the 20th embryonic day. At 1 week after hatching, CD3+ lymphocytes began to occupy the central area of the masses and His-C1+ B lymphocytes tended to be located in the periphery. Ultrastructurally, M cells were found neither in the epithelium of the mucosa nor in that of the excretory duct close to the lymphoid masses. In the deep proventricular gland, the lymphoid masses had a germinal center consisting of B lymphocytes, surrounded by the T lymphocyte-rich periphery. These masses were first recognized at the 3rd post-hatching week, presumably being formed against possible antigens invading into the lumen of the proventricular gland. On the other hand, the lymphoid masses beneath the surface epithelium and those near the duct orifice existing before the hatching period were considered to be prepared to establish the local mucosal immune barriers against the expectant antigenic invasion.     

Are there M cells in the cecal tonsil of chickens?

A unique morphological cell type, "microfold or membranous (M) cell-like cell", was detected electron-microscopically in the cecal tonsil epithelium of the chicken. M cell-like cells possessed a few short microvilli of irregular arrangement and a large number of lymphocytes and macrophages wedged into their basal surfaces. Triticum vulgaris was found to bind to M cell-like cells. With horseradish peroxidase (HRP) treatment, M cell-like cells showed an active HRP uptake just as did the neighbouring usual absorptive epithelial cells. No uptake of colloidal carbon particles from the intestinal lumen was recognized in any part of the intestinal epithelium. These results suggest that M cell-like cells of the chicken possess some M cell-characteristic morphological and histochemical features, but that their active uptake of foreign materials is not so developed as in mammalian M cells.     

Differentiation of epithelial cells to M cells in response to bacterial colonization on the follicle-associated epithelium of Peyer's patch in rat small intestine

To clarify the relationship between M cells and intestinal microflora, histoplanimetrical investigation into the bacterial colonization and the differentiation to M cells was carried out in rat Peyer's patch under physiological conditions. The follicle-associated epithelium (FAE), except for the narrow area of apical region, was closely covered with both neighboring intestinal villi and a thick mucous layer, the latter of which also filled the intervillous spaces as well as the space between the FAE and the neighboring intestinal villi. Indigenous bacteria adhered almost constantly to the narrow areas of apical regions of both intestinal villi and the FAE. Bacterial colonies were occasionally located on the basal to middle region of FAE, where M cells also appeared, forming large pockets. When bacterial colonies were located on the basal to middle region of FAE, bacteria with the same morphological characteristics also proliferated in the intervillous spaces neighboring the Peyer's patch. In cases with no bacterial colonies on the basal to middle region of FAE, however, M cells were rare in the FAE. Histoplanimetrical analysis showed the similar distribution pattern of bacterial colonies on the FAE and M cells in the FAE. M cells ultrastructurally engulfed indigenous bacteria, which were then transported to the pockets. These results suggest that indigenous bacterial colonization on the FAE stimulates the differentiation of M cells in the FAE under physiological conditions. The uptake of bacteria by M cells might contribute the regulation of the development of indigenous bacterial colonies in the small intestine.     

Interactions of butyric acid- and acetic acid-treated Salmonella with chicken primary cecal epithelial cells in vitro

In vitro studies of the interaction between pathogenic bacteria and the chicken intestinal epithelium are hampered by the lack of a host- and tissue-specific in vitro model. Therefore, a reproducible method for isolation and cultivation of chicken primary cecal epithelial cells was developed. Cecal crypts were isolated and cultured in vitro to form a semiconfluent layer of epithelial cells. Incubation of Salmonella enteritidis with these cells resulted in invasion. Pretreatment of the Salmonella bacteria with butyric acid resulted in a significant decrease of invasion of the bacteria in the chicken cecal epithelial cells, whereas pretreatment with acetic acid increased invasiveness. These interactions of S. enteritidis with primary chicken cecal epithelial cells were similar to the interactions with other epithelial cell types.     

M cells and associated lymphoid tissue of the equine nasopharyngeal tonsil

The aim of this study was to characterise the morphological and histochemical features of equine nasopharyngeal tonsillar tissue. Nasal and oropharyngeal tonsillar tissue has been described as the gatekeeper to mucosal immunity because of its strategic location at the entrance to the respiratory and alimentary tracts. A combination of light, scanning and transmission electron microscopy has revealed the presence of follicle-associated epithelium (FAE) overlying lymphoid tissue of the equine nasopharyngeal tonsil caudal to the pharyngeal opening of the guttural pouch. Membranous microvillus (M) cells were identified in the FAE on the basis of short microvilli, an intimate association with lymphocytes, cytoplasmic vimentin filaments and epitopes on the apical surface reactive with lectin GS I-B4 specific for alpha-linked galactose. CD4-positive lymphocytes were scattered throughout the lamina propria mucosae as well as forming dense aggregates in the subepithelial part. The central follicular area was heavily populated with B lymphocytes and the dome and parafollicular areas contained both CD4- and CD8-positive lymphocytes. CD8-positive lymphocytes were also present in the epithelium and, together with B lymphocytes, in small numbers in the lamina propria mucosae. These observations indicate that the nasopharyngeal tonsil is potentially an important mucosal immune induction site in the horse and an appropriate target for intranasally administered vaccines.     

Dome epithelial M cells dissociated from rabbit gut-associated lymphoid tissues

Dome and dome epithelial cells were selectively dissociated from gut-associated lymphoid tissues of rabbits. Sequential tissue washes in dithiothreitol, EDTA, and collagenase removed the dome epithelium, without disrupting the follicles or villi, and provided a cell suspension containing 74 +/- 6% lymphocytes, 9 +/- 4% columnar epithelial cells, 10 +/- 7% tangible-body macrophages, and 4 +/- 2% M cells (follicle-associated epithelial cells). The last mentioned cells were characterized by transmission electron microscopy as large (20 to 55 microns diameter) cuboidal, round, or oval cells with eccentric nuclei and thin membranous processes surrounding empty vacuoles. The M cells were occasionally joined together by tight junctions. Histochemical and immunocytochemical analyses of M cells with the light microscope showed that they were devoid of immunoglobulins and negative for T-cell antigen and secretory component and had no detectable alkaline phosphatase or endogenous peroxidase activity. The M cells had few vacuoles with faint acid phosphatase activity; nonspecific neutral esterase was abundant. Possible uses for dome and dome epithelial cells are discussed.     

Lymphocyte subsets in the mammary gland of sows

The presence and localisation of lymphocyte subsets together with class II bearing cells in the mammary gland of sows, were studied at different periods of the reproductive cycle by immunohistochemistry and compared with blood. All cell types involved in the immune response were present in the mammary gland at the different stages of gestation and lactation and nearer the alveolar epithelium as gestation proceeded: T lymphocytes, including CD4+ and CD8+, B lymphocytes and class II bearing cells (epithelial cells and macrophages). The results indicated an early accumulation of T lymphocytes, specifically T helper cells, during pregnancy; the specific increase of IgA lymphocytes occurring after this phase could suggest a role for these T cells in the induction of IgA response. The local accumulation of immune cells sustains the view that the mammary gland is able to mount a true local immune response and the increase in CD8+ cells near the epithelium suggests a role in local immune defence.     

Ultrastructural study on the epithelial responses against attachment of indigenous bacteria to epithelial membranes in peyer's patches of rat small intestine

The ultrastructure of epithelial responses against the membrane adhesion of indigenous bacteria was investigated in the follicle-associated epithelium (FAE) of rat small intestine. The most frequent adherence of the various morphological types of bacteria to the epithelial membranes was found at the apex of the FAE. The attachment sites were deeply invaginated, and their bottoms were deformed into a sharp cone shape. Four layers with different electron densities were formed just beneath the apical membranes by microfilaments which surrounded the invaginations. The electron density of each layer was gradually decreased as being apart from the invaginations. The extremities of some bacteria in the invaginations were deformed into sharpened shapes. The cell walls of the extremities of the bacteria were occasionally dissolved in the invaginations, and their cytoplasms were slightly swollen with low electron densities. In some invaginations, the attached bacteria were eliminated to leave their fragments such as filamentous debris and a part of cell walls. Finally these remnants disappeared completely. When the bacterial colonies existed in the middle region of the FAE, the attachment of bacteria resulted in the engulfment of bacteria by M cells. The degenerated bacteria whose cytoplasmic matrices were separated into high electron dense materials and cleared materials were occasionally engulfed by ordinary microvillous columnar epithelial cells or goblet cells throughout the FAE. These findings suggest that the epithelial cells reject the attachment of live indigenous bacteria and that the M cells absorb indigenous bacteria in rat Peyer's patches.     

Electron microscopic studies on conjunctiva associated lymphoid tissue (CALT) in Angora goats

The purpose of this study was to investigate the electron microscopic structure of conjunctiva associated lymphoid tissue (CALT) and to determine the uptake of macromolecules from follicle associated epithelium (FAE) of Angora goats. The sample tissues taken from lower and upper eyelids of ten 5-6 month-old healthy Angora goats were used in this study. The conjunctiva associated lymphoid tissue of Angora goats was formed by solitary or aggregate lymphoid follicle and follicle associated epithelium which cover these follicle. FAE was formed by flattened epithelial cells, lymphocytes, monocytes and polymorph nuclear leukocytes but no goblet cells. Ferritin particles were seen on the apical surface, in the invaginations, vesicles, vacuoles of flattened epithelial cells. It was concluded that these epithelial cells were specialized to uptake macromolecules.     

Differences in lectin-binding properties between the common mucosal epithelium and follicle-associated epithelium in the rabbit small intestine

Differences in sugar distribution between the villous epithelium and follicle-associated epithelium (FAE) were compared using lectins in the rabbit small intestine. In every portion, villous columnar epithelial cells primarily exhibited a positive reaction to the GalNAc, GlcNAc, galactose, and oligosaccharide. In the ileal Peyer's patch (PP), whereas microvillous epithelial cells exhibited positive reactions, M cells tended to be negative. The villous epithelial reaction to the fucose group was negative, but M cells and microvillous epithelial cells showed a positive to the fucose. No epithelium had a positive reaction to the mannose and glucose. The variety of lectin-binding properties of villous epithelial cells and M cells may reflect specificity for the recognizing luminal substances such as antigenic molecules and bacterial elements.     

Immunocytochemical demonstration of lymphocyte subsets and MHC class II antigen expression in synovial membranes from dogs with rheumatoid arthritis and degenerative joint disease

The study describes the distribution of canine leucocyte antigens in synovial membrane biopsies from six dogs with canine rheumatoid arthritis (CRA) and from eight dogs with osteoarthritis (OA) secondary to spontaneous rupture of the cranial cruciate ligament (CCL) (n = 5) or patellar luxation (n = 3). Synovial membranes from five dogs without evidence of joint lesions were used as control tissues. In the subsynovium of dogs with normal joints CD5+, CD4+, CD8+ and alpha beta TCR+ lymphocytes were present only in low numbers. With monoclonal antibody (mAb) to MHC class II antigen, either none or up to 20-30% of synovial lining cells were immunoreactive. Furthermore, scattered MHCII+ stromal cells were seen in the deeper subsynovial layer. In synovial membrane biopsies from dogs with CRA numerous diffusely and perivascularly distributed CD5+ lymphocytes were found in the subsynovium. CD4+ cells outnumbered CD8+ cells and were more numerous in the perivascular areas. In all the CRA cases examined, there were markedly higher numbers of alpha beta TCR+ cells compared with gamma delta TCR+ cells. With mAb to CD21, low numbers of immunoreactive lymphocytes were demonstrated. In all the CRA cases, a marked increase of MHC class II antigen expression was noted. In the majority of samples, 50% or more than 90% of the synovial lining cells were strongly MHC class II+. Throughout the subsynovial layer there were numerous MHC class II+ cells and included those with dendritic morphology and inflammatory mononuclear cells. Furthermore, marked perivascular immunoreactivity for MHC class II antigen was found. In biopsies from dogs with OA, there were markedly lower numbers of subsynovial CD5+, CD4+ and CD8+ lymphocytes. T-cells were mainly diffusely distributed. In three of the eight OA dogs examined, there was an increased percentage of synovial lining cells expressing MHC class II. The majority of OA cases had subsynovial major histocompatibility complex (MHC) class II+ cells with a dendritic morphology.     

The Epithelium Covering Peyer’s Patches in Young Milk-Fed Calves: An Ultrastructural and Enzyme Histochemical Investigation

Between the ordinary villi over Peyer’s patches there are small domes or “pseudovilli” caused by bulges in the lymphoid tissue. These “pseudovilli” were studied in 5 healthy milk-fed, about 3-week-old, pre-ruminant calves. Scanning electron microscopy revealed that the “pseudovilli” were covered by a specialized follicle associated epithelium (FAE). The FAE had poorly developed microvilli and often extensive folding of the cell surface close to the cell borders. By transmission electron microscopy the tips of the marginal folds of the FAE seemed to fuse, probably in the process of enfolding bulk material from the lumen. The FAE apical cytoplasm contained numerous thick-walled and bristle-coated invaginations, tubules and vesicles indicative of micropinocytosis. Multivesicular bodies and large vacuoles were frequent. Indications of extracellular unloading of residual bodies were found. Intraepithelial lymphocytes tended to group together, and some were rich in rough endoplasmic reticulum. Enzyme histochemistry showed weak reactions of adenosine triphosphate splitting enzyme and aminopeptidase in the FAE luminal cell border. Cytoplasmic acid phosrphatase showed a marked basal-apical decrease along the “pseudovillus” probably caused by the onset of endocytosis. The results of this study appear compatible with the concept that the FAE takes up macromolecules from the lumen by pinocytosis and sensitizes lymphocytes.     

The identification of intestinal M cells in the sacculus rotundus and appendix of the Angora rabbit

The present study was aimed at the immunohistochemical demonstration of M cells, found in the follicle-associated epithelium (FAE) of the sacculus rotundus (SR) and appendix of the Angora rabbit, using anti-vimentin primary antibodies, and at the determination of certain fine structural characteristics. Ten adult Angora rabbits constituted the material of the study. Immunohistochemical staining revealed that many cells composing the FAE, which covered the dome regions of the SR and appendix, reacted positively with vimentin. FAE contained two different types of vimentin-positive cells. The first type surrounded intraepithelial lymphocytes (IEL) with a basolateral invagination in the apex and periphery of the dome epithelium, whilst the second type consisted of columnar cells found in the FAE near crypts. The immunoreactivity of the cells found in the FAE covering the apex and periphery of the domes was observed particularly in the perinuclear cytoplasm and the cytoplasm surrounding the IEL. Electron microscopic examination demonstrated that the M cells found in the FAE covering the apex and periphery of the dome regions of the SR and appendix did not exhibit any microvilli on their apical surface. The FAE near crypts contained columnar cells, which resembled enterocytes. The apical membrane of these cells exhibited shorter and irregular microvilli, in contrast to neighbouring enterocytes. It was determined that M cells, found in the FAE of the SR and appendix in the Angora rabbit, displayed similarities in terms of localization and fine structure. This situation may be indicative of the two lymphoid structures with different localization having similar functional properties.     

Antigen-specific proliferation and activation of peripheral blood mononuclear cells from Mycobacterium bovis-infected reindeer

To evaluate antigen-specific proliferative and activation-associated responses from Mycobacterium bovis-infected reindeer, blood mononuclear cells from M. bovis- (n = 10) and non-infected reindeer (n = 4) were stimulated with a recombinant early secretory antigenic target-6 and culture filtrate protein-10 fusion protein (rESAT6:CFP10), M. bovis purified protein derivative, pokeweed mitogen, or medium alone and evaluated by flow cytometry using dye tracker analysis and cell surface marker staining. gammadelta TCR+ and CD8+ cells, but not CD4+ cells, from M. bovis-infected reindeer proliferated in response to specific antigen stimulation. Expression (i.e., mean fluorescence intensity) of CD44 was increased and CD62L decreased on proliferative as compared to non-proliferative fractions in antigen- and mitogen-stimulated cultures. In response rESAT6:CFP10 stimulation, MHC II fluorescence intensity was increased on CD4+, gammadelta TCR+, CD172a+, and IgM+ cells from infected reindeer as compared to that of non-stimulated cells from the same reindeer. Recombinant ESAT6:CFP10 stimulation also induced expansion of a CD172a+, MHC II+ population within mononuclear cell cultures from M. bovis-infected reindeer. Despite a moderate challenge dose and extended duration of incubation, experimental infection of reindeer was generally limited to lymph nodes draining the inoculation site, suggestive of host resistance to progressive disease. Present in vitro findings, therefore, may be predictive of host responses by reindeer that limit progression to disseminated disease.