We investigated the mechanisms of specific immune unresponsiveness to microfilarial antigens. The blood of patients with obvious Brugia malayi infections contains an adherent cell type that specifically suppresses reactions to microfilarial antigens but not to other antigens. In the absence of continued stimulation by parasite antigens, this suppressor cell loses its functional activity after overnight culture in vitro. Furthermore, serums from patients with and without microfilaremia contain factors that also suppress reactions to filarial antigens in vitro. These results suggest that immune unresponsiveness in human beings with patent filarial infections is due to active suppression of immune responses directed against the parasite and not to an intrinsic inability of infected patients to react to parasite antigens.

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Immune responses to parasite antigens are much lower in patients with microfilaremia than in persons with other manifestations of brugian filariasis. To determine whether hyporeactivity is associated with changes in populations of lymphocytes that regulate immune responses, we quantitated helper and suppressor T cells in the blood of patients infected with Brugia malayi. Increased numbers of suppressor T cells were present in 15 of 17 patients with microfilaremia and in six of 11 patients with elephantiasis. This increase correlated with hyporeactivity to filarial antigens but not to nonparasite antigens. Removal of suppressor T cells activated in vivo or in vitro improved reactivity to filarial antigens. These results suggest that immunosuppression induced by filarial parasites is a possible mechanism of survival of these organisms in an immunocompetent host.

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Rickettsia typhi and R. felis, etiologic agents of murine typhus and fleaborne spotted fever, respectively, were detected in Oriental rat fleas (Xenopsylla cheopis) collected from rodents and shrews in Java, Indonesia. We describe the first evidence of R. felis in Indonesia and naturally occurring R. felis in Oriental rat fleas.M urine typhus (endemic typhus, fleaborne typhus), caused by Rickettsia typhi, is transmitted to humans by infected fleas and is relatively common wherever susceptible rodent hosts reside (1). Fleaborne spotted fever (cat flea typhus), caused by Rickettsia felis, is another zoonotic disease carried by fleas and appears to have an equally wide, cosmopolitan distribution; human infections with R. felis have a clinical syndrome similar to that of murine typhus (1-4). The cat flea, Ctenocephalides felis, has been identified as the primary arthropod vector of R. felis in North and South America (United States, Mexico, Peru, Brazil), Europe (Spain, France, United Kingdom, Cyprus), Africa (Gabon, Ethiopia), Asia (Thailand, Afghanistan, Israel), Australia, and New Zealand (1,5-10). We describe the first evidence of R. felis in Indonesia and apparent natural infections of R. felis in the Oriental rat flea, Xenopsylla cheopis, implicating this flea species for the first time as a potential vector for fleaborne spotted fever. The StudySamples of X. cheopis were collected from 39 live-captured, peridomestic rodents and shrews from 3 localities in Malang, East Java, Indonesia, during an epidemiologic study conducted in 1994 (11). In this study the fleas were reidentified by using morphologic criteria, stored in fresh 70% ethanol, and subsequently evaluated for the presence of rickettsial DNA. DNA sample preparations were derived from triturates of 103 individual fleas in 100 µL PrepManUltra sample preparation reagent (Applied Biosystems, Foster City, CA, USA). DNA preparations of 1 to 5 fleas collected from the same rodent were pooled for testing. Reaction mixtures for the quantitative real-time PCR (qPCR) assays had a total volume of 25 µL and contained 3 µL DNA template. The master mixes were prepared for the 17-kDa Rickettsia-, R. typhi-and R. felis-specific qPCR assays in a separate, clean (DNA-free) room as previously described (6,12). The primer and probe sequences for the 17-kDa Rickettsia-specific and R. felis-specific assays have been reported (6,11). The R. typhi forward (Rt557F: 5′-TGG TAT TAC TGC TCA ACA AGC T-3′) and reverse (Rt678R: 5′-CAG TAA AGT CTA TTG ATC CTA CAC C-3′) primers and probe (Rt640BP: 5′-TET-CGC GAT CGT TAA TAG CAG CAC CAG CAT TAT CGC G-DABCYL-3′) sequences are listed here. Included in each run were 3 negative controls (GIBCO Ultrapure DNA-free distilled water, Invitrogen Corporation, Grand Island, NY, USA), 1 produced in the clean room and 2 in a biosafety cabinet in another laboratory where DNA templates were added. A TOPO TA plasmid (Invitrogen Corporation) that contained the target sequence at 10 3 copies for each assay was used as a positive control. qPCR reactions w...