REDUCED ANTIFILARIAL IGG4 RESPONSIVENESS IN A SUBPOPULATION OF MICROFILAREMIC PERSONS

Antifilarial IgG4 is a marker of active filarial infection; however, 1 0% of microfilaremic persons may have low levels of antifilarial IgG4. To gain insight into how persons with microfilaremia with low antifil arial IgG4 levels (<10 mu g/mL) differ from those with high levels (>1 70 mu g/mL), total IgG4 and IgE and filaria-specific IgE, IgG1, and Ig G2 were measured by ELISA in serum samples collected from 85 microfila remic Haitians. Persons with lower levels of antifilarial IgG4 had sig nificantly lower total IgG4 and total IgE (P < .01), lower levels of a ntifilarial IgG1, IgG2, and IgE (P < .01, = .03, and < .01, respective ly), and higher antigenemia and microfilaremia (P < .01) than did pers ons with higher levels of antifilarial IgG4. Increased antigen loads i n microfilaremic persons may be associated with a down-regulation of a ntibody production, which extends to all isotypes.