Immune Responses in Human Infections with Brugia malayi: Correlation of Cellular and Humoral Reactions to Microfilarial Antigens with Clinical Status *

Abstract

We evaluated immune responses to microfilarial antigens in subjects living in an area of South Kalimantan, Indonesia where malayan filariasis is endemic. Antibodies reacting with the sheath of living Brugia malayi microfilariae were detected by indirect immunofluorescence in the sera of 36/90 patients; all but four of the sera were from subjects without detectable microfilaremia. IgG antisheath antibodies were more prevalent in patients with elephantiasis than in amicrofilaremic subjects with other stages of filariasis. Immunoglobulin was detected on microfilariae isolated from the blood of 8/26 individuals whose serum lacked antisheath antibodies. Antibodies that promote the adherence of buffy coat leukocytes from normal donors to B. malayi microfilariae were detected in 11/90 sera. All 11 positive sera were from amicrofilaremic subjects and contained high titers of IgG anti-sheath anti-bodies detected by indirect immunofluorescence. Comparison of the prevalence of antisheath antibodies with in vitro lymphocyte responses to microfilarial antigens, previously studied in the same patients, revealed that amicrofilaremic subjects exhibit either evidence of cellular immunity to microfilarial antigens or antifilarial antibodies, but usually not both. These studies reveal a striking correlation between the presence of immune responses to microfilarial antigens and the absence of patent microfilaremia, and suggest that more than one type of immune reaction might be involved in the resistance to and the elimination of filarial infections.