We explored the in vitro interaction of human peripheral blood mononuclear cells with the arthroconidial stage of the fungus Coccidioides immitis. Fresh peripheral blood monocytes in an adherent monolayer were capable of ingesting C. immitis. Further, peripheral blood monocytes from either skin-test-positive or skin-test-negative donors significantly decreased the in vitro growth of C. immitis when coccidioidal arthroconidia were incubated with monocytes. Peripheral blood mononuclear cells also reduced fungal incorporation of the chitin precursor N-acetyl glucosamine. Cell fractions consisting predominantly of monocytes were significantly more active in this regard than fractions containing predominantly lymphocytes. Moreover, this activity was independent of the coccidioidal skin-test status of the donor. We conclude that human fresh peripheral blood mononuclear cells are able to phagocytize C. immitis arthroconidia and have the ability to inhibit its growth in vitro. That these abilities are independent of the immune status of the donor supports the possibility that the peripheral blood monocyte may contribute to the early defense against initial coccidioidal infection.
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