Cytometric profile of molybdenum-induced contact sensitization versus a strong allergen reaction to oxazolone in murine auricular lymph node (ALN) test.

Induction of contact hypersensitivity (CH) by molybdenum chloride (MoCl5) was determined by auricular lymph node (ALN) test in C57B1/6 mice. The ALN test was further improved by immunophenotyping and cytometric analysis of subset-specific cell in the draining node. Skin sensitization was induced by topical ear exposure to 1.0-50% oxazolone and resulted in a strong dose-related ALN reaction. Analogous exposure to MoCl5 resulted in a weaker but marked dose-related reaction, also manifested as an increase in cell number/ALN. Other differences between the oxazolone-induced strong sensitization and the MoCl5-related ALN reaction were: (1) an increase in the total number of Ig+ cells, which was, however, unchanged in the MoCl5-exposed mice; (2) a significant increase in the total number of large/activated T-cell subsets; and (3) a marked shift in the relative percentage of gated large/activated subsets of ALN cells, which was not observed in the MoCl5-exposed animals. Thus, it appeared that the molybdenum exposure induced a nonspecific increase in the cell number/ALN and was not accompanied by any marked activation of the T-cell subsets. Immunotoxicity of a 14 day subchronic exposure to MoCl5 at 1-100 ppm in food was studied by quantification of splenic humoral IgM response to sheep erythrocytes (SRBC). Plaque-forming cells (PFC) and enzyme-linked immunosorbent assay (ELISA) revealed unchanged humoral exposure in MoCl5-exposed mice. Cytometric assay of fluorescent beads uptake showed unchanged phagocytic activity of peritoneal macrophages from the MoCl5-exposed mice. Immunophenotyping of CD4+, CD8+, Thy 1.2+ and Ig+ cells revealed no effect of MoCl5 exposure on the total count of cell subsets in the ungated populations of spleen, lymph nodes and peripheral blood cells. Molybdenum chloride should thus be considered as a non-immunotoxic and a weak, nonspecific contact irritant.