Compartments within the lymph node cortex of calves and adult cattle differ in the distribution of leukocyte populations: an immunohistochemical study using computer-assisted morphometric analysis

Natural killer cells in lymph nodes of healthy calves express CD16 and show both cytotoxic and cytokine-producing properties

Natural killer (NK) cells were recently shown to play an important immunomodulatory role in lymph nodes. We here report the presence, phenotype and function of NK cells resident in lymph nodes of several anatomical sites of healthy calves. NKp46+/CD3-lymphocytes, recently demonstrated to precisely identify NK cells in all tested species, were present in the paracortex and the medulla of bovine lymph nodes. Most lymph node-derived NK cells expressed CD16 and perforin, and a lytic capacity was demonstrated, while a well-developed interferon-gamma response to interleukin-2 and interleukin-12 stimulation was also seen. Lymph node-derived NK cells differed from those in blood by a higher expression of the activation markers CD44 and CD25, as well as CD8. L-selectin (CD62L) was expressed by the majority of lymph node-derived NK cells, consistent with a dependency of this molecule for migration to lymph nodes. Unlike in blood, the majority of lymph node NK cells had little or no CD2 expression. Compared to available literature, calf lymph nodes contained NK cells in numbers equal to or higher than reported in humans, and clearly higher than in mice. These findings suggest a cytotoxic role of lymph node residing NK cells, beyond the predominantly cytokine-producing role previously inferred from studies on human NK cells.

Age-dependent differences in cytokine and antibody responses after experimental RSV infection in a bovine model

Respiratory syncytial virus (RSV) causes severe respiratory disease in both infants and calves. As in humans, bovine RSV (BRSV) infections are most severe in the first 6 months of life. In this study, experimental infection with BRSV was performed in calves aged 1-5, 9-16 or 32-37 weeks. Compared to younger animals, older calves showed significantly less fever and lower TNFalpha levels and less virus-specific IFNgamma release. In addition, blood from older animals had more mononuclear cells, more B cells and stronger BRSV-specific IgA and neutralising antibody responses to infection. A strong "inflammatory" but weak humoral antiviral response in very young animals suggests that enhanced inflammation contributes to disease during RSV infection during the early postnatal period.

Comparison of flow cytometry and image morphometry in the quantitative analysis of cell population markers in the lymph node of sheep

Two approaches to the quantitative analysis of cell population markers in tissues are flow cytometry and image morphometry. To compare these methods, sheep lymph nodes were collected and analysed for CD8+ and CD21+ cell populations, which were selected to represent dispersed and concentrated cell populations, respectively. These two populations were measured as a percentage of total cell count (flow) or total tissue area (morphometry). The two populations were also measured as a percentage of respective base populations (CD2+ cells for CD8 and MHC II+ cells for CD21). A simple linear regression analysis showed that when the cell populations were assessed as a percentage of total cell count or total area, measurements obtained with flow and morphometry only correlated significantly with the dispersed CD8+ population and not with the highly concentrated CD21+ population. However, when the cell populations were assessed as a percentage of their base population, measurements obtained with flow and morphometry showed a significant correlation for both the dispersed and concentrated cell populations. This study demonstrates that measurements of lymph node cell populations obtained with the two methods are comparable, but that tissue distribution of cell populations should be considered, when the unit of measurement is chosen.

Localisation of CD25+ cells and MHCII+ cells in lymph nodes draining Mycobacterium avium subsp. paratuberculosis vaccination granuloma and the presence of a systemic immune response

Vaccination of goat kids against paratuberculosis protects against lesions and clinical disease. The systemic cellular response was studied in goat kids 3-9 weeks after vaccination. Peripheral blood cells showed increased interferon-gamma production and expression of interleukin-2 receptor (CD25) after stimulation with Mycobacterium avium subsp. paratuberculosis antigens. The lymph node draining the vaccination granuloma was studied three weeks after vaccination in a parallel group of goat kids. In deep cortex, MHCII+ cells were observed surrounded by CD4+ T-cells, while follicular hypertrophy and hyperplasia were prominent in the subcapsular region and along connective tissue trabecula. Comparison of the local and systemic immune responses revealed an inverse relationship between CD25+ T-cells in the lymph node deep cortex and cells in peripheral blood that up-regulate CD25 upon in vitro stimulation, suggesting that activated and regulatory T-cells in the local lymph node influence the level of circulating antigen-specific T-cells following vaccination against paratuberculosis in goats.

Eimeria infections in cows in the periparturient phase and their calves: oocyst excretion and levels of specific serum and colostrum antibodies

Faecal Eimeria oocyst excretion and levels of antibodies to first generation merozoite antigen of E. bovis in sera and colostra were followed in 86 and 70 cow-calf pairs in northern (group EF) and central Germany (group H), respectively, over periods of 3 weeks before to 3 weeks after calving in cows and from birth to an age of 63 days in calves. Oocysts were found in 30 and 7.7% of cows in groups EF and H, respectively. They belonged to 10 (group EF) and four Eimeria spp. (group H) with E. bovis, E. ellipsoidalis, E. auburnensis and E. zuerni as the most frequently occurring species. Prevalence and intensity of oocyst excretion varied with time resulting in peak values around the date of parturition, particularly in the case of E. bovis. Peak values at the time of parturition were also seen in case of strongyle egg excretion. Seven (group H) and nine Eimeria spp. (group EF) were found in the calves. The predominant species E. ellipsoidalis, E. zuerni, E. bovis and E. auburnensis were detected for the first time earlier after birth (3-5 weeks) than the others. The prevalence of Eimeria infections increased to 67.1% (group EF) and 50.1% (group H) 9 weeks after birth. Specific IgM and IgA antibody levels (the latter only determined in group EF) in cow sera remained almost constant throughout the observation period, whereas IgG(1) and IgG(2) levels were reduced at the time of parturition. Levels of specific antibodies in sera and colostra were significantly correlated. Except IgM antibodies, significant inverse correlations were found in cows between intensity of infection with E. bovis and specific serum IgG (group H) and IgG(2) (group EF) antibodies. Antibodies to E. bovis were detected in calves sera only after colostrum intake with significant correlations between levels in calves sera and colostra. Levels decreased, starting within the first week of life (most conspicuously in case of IgM and IgA) until the third week. Subsequently, but except IgG(1) antibody concentrations increased until the end of the observation period. Interrelations between antibody levels and the total amount of E. bovis oocysts excreted by the calves until the ninth week of life varied with the age of the animals. Inverse relationships in the first 3 weeks of life as suggested by negative correlation coefficients could not be proven statistically. Thus, there is no unambiguous proof for immunoprotection of calves against E. bovis via maternal immunity. Considering antibody levels in the 3-9 weeks old calves significant direct correlations with E. bovis oocyst excretion were found in case of IgM, IgG(2) and IgA, reflecting an active immune response of young calves to coccidial infection.

Effect of early fetal splenectomy on prenatal B-cell development in sheep

The contribution of early splenic B-cell populations to the colonization of the ileal Peyer's patch was investigated following the surgical removal of the spleen in a series of 56-day-old fetal sheep. The fetuses were killed at 140 days of gestation and the ileal Peyer's patch, the distal jejunal lymph node which drains the Peyer's patch, and a peripheral lymph node, the superficial cervical lymph node, were examined. Enzyme and immunohistochemical evaluation concluded that the distribution of B cells, T cells and stromal cells in the ileal Peyer's patch was similar in splenectomized and normal fetal sheep. Thus, the presence of the fetal spleen was not essential for the colonization of the ileal Peyer's patch and other early sites of B-cell accumulation would appear capable of generating the necessary precursor populations. Investigation of B-cell populations in lymph nodes used a combination of terminal deoxynucleotidyl-transferase-mediated deoxyuridine-triphosphate nick-end-labelling (TUNEL) histochemistry and immunofluorescence to determine the average number of apoptotic B cells in the primary follicles of the outer cortex of splenectomized and normal lambs. A significantly increased number of apoptotic B cells was present in the distal jejunal lymph node but not in the superficial cervical lymph node of splenectomized lambs. This finding suggests that splenectomy affected prenatal B-cell development in fetal sheep and raises questions as to the regulation of B-cell lymphopoiesis in a species using a post-rearrangement organ of diversification.

Accessory cell populations in draining lymph nodes of lambs in the elicitation phase of DNCB-induced contact hypersensitivity

The effect of experimentally induced contact hypersensitivity on accessory cell populations in draining lymph nodes of lambs was studied. Previous studies of draining lymph nodes of lambs during the elicitation phase of CHS have shown that there are significant changes in T-cell subpopulations, particularly CD4(+) cells and gamma delta T-cells, but the behaviour of accessory (antigen presenting) cell populations was not investigated. The immunohistochemical presence of accessory cell populations was determined using markers for CD68, Pan MHCII, MHCII DQ, MHCII DR, OvCD1w1 (putative human CD1a/c-like) and OvCD1w2 (human CD1b-like). Ten lambs were sensitised, and 14 days later re-challenged, by applying the hapten di-nitro-chloro-benzene (DNCB) together with an acetone and olive oil (AOO) vehicle, onto the skin. Cryosections of the draining lymph nodes were stained immunohistochemically for the accessory cell markers. Using an image analysis system, the areas of staining in the lymph nodes from the challenged animals were compared with measurements in control animals. A significant increase in staining for CD68(+) cells was detected in the cortex of the DNCB-treated group (p=0.003). A significant increase in staining for the Pan MHCII marker was also observed in the DNCB group (p=0. 013). These results show that MHCII(+) cells and CD68(+) cells constitute a prominent cell population in the cortex of the regional lymph nodes of lambs in the late elicitation phase of DNCB-induced contact hypersensitivity.

Distribution of MHC-II and CD1 molecules in the skin of lambs and changes during experimentally-induced contact hypersensitivity

The presentation of antigen to specific T-cell populations is a crucial event during the elicitation phase of contact hypersensitivity (CHS). Significant changes in CD4(+) T-cell and gammadelta T-cell populations occur in the skin of sheep 48h after re-exposure to dinitrochlorobenzene but the expression of antigen presentation molecules such as MHC-II and CD1 at this stage of the hypersensitivity response has not been investigated. In the present study, a panel of monoclonal antibodies recognising CD1 and MHC-II subtypes was used in combination with computer assisted morphometric analysis to estimate the distribution of antigen presentation molecules in the superficial and deep dermis of the ears of lambs during the elicitation phase of CHS. The MHC-II molecules showed predominantly a perivascular and peri-appendageal distribution in the dermis and there were scattered MHC-II(+) cells in the basal and suprabasal layers of the epidermis. The CD1w2(+) (CD1b-like) molecules were present on distinct cells that were scattered evenly through the dermis, whereas CD1w3(+) (CD1c-like) molecules were almost exclusively detected on or in close association with the vascular endothelium. There was a significant increase in the presence of MHC-DQ(+) cells in the superficial dermis of dinitrochlorobenzene-treated animals compared with both an untreated control group and a vehicle-treated control group. However, MHC-DQ/DR(+) and CD1w3(+) cells only showed a significant increase compared with the vehicle-treated control group. The present study shows that the distribution of molecules involved in antigen presentation to CD4(+) T-cells and gammadelta T-cells changes during the elicitation phase of CHS in sheep, and suggests a role for MHC-DQ molecules on antigen presenting cells. However, the changes in distribution and expression of MHC-II and CD1 subtypes argue against a prominent role for a CD1-dependent pathway for T-cell recognition in the clinical cutaneous hypersensitivity response in sheep. Based on the expression of MHC-II molecules and CD1c molecules, we also suggest a potential role for endothelial cells in antigen presentation during the clinical dermatitis reaction.

Increased gammadelta T-cell populations in draining lymph nodes of lambs during the elicitation phase of dinitrochlorobenzene-induced contact hypersensitivity

Ten lambs were sensitised with the hapten DNCB in an acetone/olive oil vehicle. The hapten/vehicle solution was applied onto the skin on the shaved ventral surface of the right ear. Two weeks later these lambs were rechallenged with the DNCB/vehicle solution. Simultaneously, ten non-sensitised lambs were treated with vehicle only, serving as vehicle controls. The 20 lambs were slaughtered 48 h after challenge/vehicle treatment, along with ten untreated animals serving as normal controls. Specimens of draining lymph nodes were collected from the 30 animals. All lambs were between 149 and 187 days old. Lymph node cryosections were stained for several leukocyte markers using monoclonal antibodies with the ABC immunohistochemical method. The stained sections were subsequently assessed in three different cortical compartments in each section, using an image analysis system. The resulting measurements from the three groups were compared. A marked increase of gammadelta T cells was detected in the DNCB group. The number of CD4+ T helper cells was decreased in the DNCB group compared with the normal control group, but not with the vehicle control group. No differences were revealed for CD8+ T cytotoxic cells or B cells. These findings were interpreted to be the consequences of possible downregulatory mechanisms protecting the lymphoid tissue from hypersensitivity. The prominence of gammadelta T-cells could indicate that these cells are involved in downregulation.