High levels of parasite-specific IgG1 correlate with the amicrofilaremic state in Loa loa infection.

To investigate the mechanisms of protective immunity operating in Loa loa infection, 56 persons from a L. ioa-endemic village in southeast Gabon were examined over a 7-year period. The level of L. loa-specific IgG subclasses in defined parasitologic groups was compared by use of ELISA with either adult, microfilarial, or third-stage larval (L3) antigens of L. loa. With all antigen preparations, IgG1 levels were significantly higher in amicrofilaremic persons than in persons with high or low levels of microfilariae. Moreover, there was a significant negative correlation between IgG1 levels to L3 antigen and the density of microfilariae (Spearman's r(s) = -.701; P < .01). There was no correlation between density of microfilariae and levels of other IgG subclasses or of IgE. These data indicate that IgG1 may play a role in the effector mechanism(s) involved in resistance against L. loa and suggest that L3 antigens may be important in eliciting protective responses.