Bifenthrin activates homotypic aggregation in human T-cell lines.

BACKGROUND: Here, we addressed the concern that, despite the lack of overt toxicity, exposure to low levels of the common household pyrethroid pesticide, bifenthrin, could cause harm to the immune system. To do this, we measure the effect of bifenthrin on phytohemagglutinin (PHA) activation of homotypic aggregation in human T-cell lines. MATERIAL/
METHODS: The human CD4+ H9, and Jurkat cell lines and the human promonocyte U937 cell line, were exposed to varying concentrations of bifenthrin. Cell viability was determined using the AlmarBlue Toxicity Assay. Concentrations of bifenthrin which did not reduce cell viability were determined and these concentrations were tested for the effect of bifenthrin on PHA-mediated homotypic aggregation. Blocking antibodies to ICAM and LFA-1 were used to disrupt aggregation and a nonspecific IgG was used as a control.
RESULTS: Bifenthrin was found to be nontoxic at concentrations ranging from 10(-4) to 10(-13) M. Bifenthrin did not inhibit PHA induced cell aggregation in all cell lines tested. However, at 10(-4) M, bifenthrin to form aggregates stimulated homotypic aggregation in the H9 and Jurkat T-cell lines. The bifenthrin-induced aggregate formation, like that seen with PHA, was blocked by treating the cells with antibodies to either LFA-1 or ICAM.
CONCLUSIONS: The results here show that bifenthrin activates T-cell function by stimulating ICAM/LFA-1 mediated homotypic aggregation. This data suggests that exposure to bifenthrin, even at "acceptable" limits, can increase the risk for and frequency of inflammatory responses and diseases such as asthma.