Surface markers on bovine fetal lymphocytes and immunoglobulin synthesis in a congenital infection related to epizootic bovine abortion.

Immunological parameters were studied among 23 late-term bovine fetuses. Epizootic bovine abortion (EBA) disease was induced in fetuses by feeding Ornithodoros coriaceus ticks on pregnant heifers. A spirochaete-like microorganism was detected in the blood of diseased fetuses and in inapparent natural infections in some abattoir-collected fetuses. Fetuses were classified according to stages of disease: EBA diseased (n = 10), EBA infected (n = 7) and normal (n = 6). Using flow cytometry, the presence of surface immunoglobulins (sIg) and peanut agglutinin (PNA) receptors were used to detect B and T lymphocytes, respectively. In peripheral blood of normal fetuses, most lymphocytes were identified as T or B cells, whereas about 20 per cent of lymphocytes in EBA diseased fetuses did not reveal the sIg or PNA receptor markers (null cells). Size and shape analyses by flow cytometry detected a population of enlarged lymphocytes in the EBA diseased fetuses. The numbers of cells bearing determinants reactive with monoclonal antibodies specific for bovine T cells (B26A and B29A) and B cells (TH21A) were considerably less than those expressing the PNA receptor and sIg. These results suggested that the monoclonal antibodies were binding to differentiation antigens which were not consistently expressed on the fetal cells. Radio-immunodiffusion was used to measure bovine IgM, IgG1 and IgG2 in fetal serum. The quantities of immunoglobulins were markedly increased in animals infected with the spirochaete-like organism (groups 1 and 2) and were assumed to result from fetal antibody synthesis.