Identification of cell types present in bovine haemolymph nodes and lymph nodes by immunostaining

Mediastinal haemolymph nodes (HN) and lymph nodes (LN) of 15 healthy calves and ten healthy steers and 53 steers with respiratory diseases (pneumonias) were studied using monoclonal antibodies (Mabs) specific to bovine B and T lymphocytes: BAQ155A (B), CH128A (BoCD2), CACT138A (BoCD4), CACT80 (BoCD8), BAQ4A (Null cells). Topographical distribution of the HN T and B cell subset appears similar to the distributions in the LN. The germinal centres contained B+, BoCD2+ and BoCD4+ cells, whereas no staining of lymphocytes could be seen in the mantle zone. BoCD2+, BoCD4+ and BoCD8+ lymphocytes were located in the parafollicular lymphatic tissue, whereas B and Null lymphocytes were scattered. The same pattern was observed in the hyperplastic haemolymphadenitis of steers with respiratory diseases with an increased positive staining for BoCD4 and BoCD8. A similar pattern was observed for HN and LN Immunoglobulin Containing Cells (ICC). Furthermore, in the calf HN, IgM positive ICC were the most frequent class (44% in HN vs. 33% in LN). It is likely that they could contribute to produce a particularly efficient primary immune response. This is the first study of the distribution of different lymphocyte phenotypes in mammalian haemolymph nodes.