CYTOMETRIC PROFILE OF MOLYBDENUM-INDUCED CONTACT SENSITIZATION VERSUSA STRONG ALLERGEN REACTION TO OXAZOLONE IN MURINE AURICULAR LYMPH-NODE (ALN) TEST

Induction of contact hypersensitivity (CH) by molybdenum chloride (MoC l5) 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 cells in the draining node. Skin sensitiz ation was induced by topical ear exposure to 1.0-5.0% oxazolone and re sulted in a strong dose-related ALN reaction. Analogous exposure to Mo Cl5 resulted in a weaker but marked dose-related reaction, also manife sted as an increase in cell number/ALN. Other differences between the oxazolone-induced strong sensitization and the MoCl5-related ALN react ion were: (1) an increase in the total number of Ig(+) cells, which wa s, however, unchanged in the MoCl5-exposed mice; (2) a significant inc rease in the total number of large/activated T-cell subsets; and (3) a marked shift in the relative percentage of gated large/activated subs ets 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 subchroni c 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) reve aled unchanged humoral exposure in MoCl5-exposed mice. Cytometric assa y 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 Mo Cl5 exposure on the total count of cell subsets in the ungated populat ions of spleen, lymph nodes and peripheral blood cells. Molybdenum chl oride should thus be considered as a nonimmunotoxic and a weak, nonspe cific contact irritant.