Protective immunity in bancroftian filariasis. Selective recognition of a 43-kD larval stage antigen by infection-free individuals in an endemic area

There is little information about naturally occurring protective immunity in individuals living in areas endemic for lymphatic filariasis, though an immunologically hyperresponsive, unin-fected group of "endemic normal " individuals that may be im-mune has been previously recognized. To analyze the nature of the hyperresponsiveness and its potential relation to a state of protective immunity in such individuals, strict clinical, parasi-tological, and serological criteria were applied to select seven "infection-free " endemic normal individuals (ENs) from a pop-ulation of 459 persons resident in an area heavily endemic for bancroftian filariasis. Immunoblot analysis was used to com-pare the qualitative antigen recognition patterns of these en-demic normal individuals to those of a group of 12 clearly infected microfilaremic individuals (MFs) from the same en-demic area. Though immunoblot analysis using microfilarial and adult stage filarial antigens revealed no distinct differences in antigen recognition patterns between the two groups, when responses to infective larval stage antigens were assessed, 7/7 (100%) of the ENs were found to recognize a 43-kD antigen that was recognized by only 1/12 (8%) of the MFs. These findings are consistent with the concept that recognition of unique larval antigens may induce protective immunity to human filarial parasites and they identify a candidate immu-nogen for further functional assessment