A cross sectional study of lead (7439921) exposed and unexposed workers was conducted using a comprehensive panel of immunologic parameters to evaluate the association between lead exposure and changes in the immune system. Studies focused particularly on determining whether the number of CD4+ T-cells was affected by lead exposure. Lead exposed workers were recruited from a large secondary lead smelter in the United States. The final study group included 145 exposed and 84 unexposed workers. The median blood lead level (BLL) was 39 micrograms/deciliter (microg/dl) among the exposed (range 15 to 55microg/dl) and the median among the unexposed group was less than 2microg/dl (range of 2 to 12microg/dl). Median zinc-protoporphyrin (ZPP) was 48 among the exposed and 17.5microg/dl among the unexposed group. No association was found between lead exposure and the percentage of CD4+ T-cells. Even though a significant interaction between age and lead exposure for the absolute number of CD4+ T-cells was noted, this finding may have been related to an increase in lymphocyte count with age in the unexposed population. In exposure response analyses among lead exposed workers, no evidence was found of a significant relationship between the number and percentage of CD4+ cells and estimates of exposure including current blood lead, ZPP, or estimated cumulative lead exposure. Lead exposed workers had a significantly lower percentage of monocytes than unexposed workers, although the magnitude of the difference was small.

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