Immune function of bovine leukocytes after in vitro exposure to selected heavy metals

Objective-To study effects of in vitro exposure of bovine leukocytes to mer cury, cadmium, and lead on phagocytosis, natural killer cell activity, and lymphocyte proliferation. Sample Population-Leukocytes from 6 nonpregnant Holstein heifers. Procedure-Leukocytes were exposed in vitro to the aforementioned metals, an d leukocyte functions were assessed. Results-Phagocytosis was suppressed by 10(-5) to 10(-7) M CdCl2 and by 10(- 5) and 10(-6) M HgCl2, but not 10(-7) M HgCl2 nor 10(-4) to 10(-6) M PbCl2. Spontaneous and concanavalin A- or phytohemagglutinin-stimulated prolifera tion of metal-treated bovine blood mononuclear cells was not significantly different from that of nontreated control cells, except for enhanced sponta neous proliferation in response to 10(-5) M HgCl2. When proliferation was e xpressed as a stimulation index, a dose-dependent increase of spontaneous p roliferation was observed in response to exposure to HgCl2 and PbCl2. Compa red with response to 10(-6) or 10(-7) M CdCl2, reduction of mitogen-induced and spontaneous proliferation was observed on exposure to 10(-5) M CdCl2. Natural killer cell activity against YAC-1 target cells, evaluated by flow cytometry, was decreased only in cells exposed to 10(-5) M HgCl2. Conclusion and Clinical Relevance-Bovine leukocytes are susceptible to the immunomodulatory effects of in vitro exposure to heavy metals at concentrat ions equal to or higher than those at which similar effects are seen for le ukocytes from most other animal species for which data are available for co mparison. Exception is phagocytosis, which is severely affected by low conc entrations of CdCl2 and HgCl2 in cattle. Reduction of defense mechanisms on exposure to metals could lead to increased susceptibility to potential pat hogens.