Elimination of erroneous results related to bovine mononuclear cell immunophenotyping by antibodies binding to Fc receptors

Blocking immunoglobulin G (IgG) binding receptors on leukocytes is an established and highly recommended preventive procedure for immunological assays. Failing to prevent such nonspecific binding can lead to erroneous results. Several studies testing different blocking reagents have been performed in murine or human cells, however, there are no specific studies on bovine cells. Our study aimed to investigate the efficiency of blocking reagents to inhibit the nonspecific binding of mouse monoclonal antibodies (mAbs) to bovine peripheral blood cells. We observed nonspecific interactions of IgG2a and IgG2b negative isotypes with bovine leukocytes, but not IgG1. We found that these nonspecific bindings could be eliminated by blocking with purified mouse IgG, whereas little or no blocking effect was observed when bovine serum or Mouse Seroblock FcR were applied. Moreover, in the absence of an efficient blocking reagent, the percentage of CD335 positive cells was significantly higher than in the group previously blocked with mouse IgG. Based on these results, and due to the lack of specific commercial blocking reagents for bovine cells, our recommendation is to use purified mouse IgG as a blocking reagent for immune assays targeting bovine leukocytes in order to enhance the accuracy of the results.