Monoclonal antibodies that distinguish bovine T and B lymphocytes

The specificities of three monoclonal antibodies (MAbs) were investigated using microcytotoxicity, fluorescence microscopy and laser flow cytometry (LFC) techniques. By microcytotoxicity, bovine thymocytes (n=4) were estimated to be 85% B26A +, 4% TH21A + and 1% H4 +. Nylon wool enriched peripheral blood T lymphocytes (n=3) were 90% B26A +, 10% TH21A + and 10% H4 +. Adherent B cell enriched fractions (n=3) were 10% B26A +, 90% TH21A + and 90% H4 +. The two fluorochrome method was used to simultaneously identify lymphocytes that were sIg + and MAb +. In these experiments, 92% of all sIg + cells were H4 +. An identical result was obtained for TH21A. 85% of all sIg − cells were B26A +. Using LFC, the mean percentages of sIg +, H4 + and TH21A + PBL (n=5) were not significantly different. B26A recognized a significantly greater population of cells, equivalent to the expected percentage of T lymphocytes. LFC also revealed two relatively discrete sizes of B26A + PBL. The larger population overlapped the size range in which sIg +, H4 +, TH21A + PBL were found. The more numerous smaller B26A + PBL were in a size range in which few sIg +, H4 + and TH21A + PBL were found. In a study of MAb reactions with PBL of 185 cows, it was shown that in 92% of the animals H4 and TH21A were positively correlated (r=+.93), when H4 and TH21A were negatively correlated with B26A (r=−.94 and r=−.92, respectively). These correlation coefficients indicate a converse relationship between B26A and both H4 and TH21A. The remaining 8% of the animals were heterogeneous in their expression of the H4 and TH21A markers but not the B26A marker. These results provide strong evidence that: 1) B26A is a pan-T lymphocyte MAb in cattle, 2) a small but significant degree of heterogeneity exists in the expression of the epitopes recognized by H4 and TH21A. However, both MAbs recognize all B lymphocytes of most individuals, and 3) using a variety of immunological methods these three MAbs can now reliably be used to assay bovine T and B lymphocytes.