Setsuko Tsukidate

Down-regulation of murine susceptibility to cerebral malaria by inoculation with third-stage larvae of the filarial nematode Brugia pahangi.

In areas where malaria is endemic, helminthic infections, caused by intestinal or filarial parasites, commonly coexist with malaria in the same individual. This study investigates the course of Plasmodium berghei malaria infection in CBA/J mice inoculated with irradiated attenuated 3rd-stage larvae (L3) of Brugia pahangi. Peripheral eosinophil counts, serum IgE levels and cytokine production revealed that the filarial antigen induced T-helper type 2 (Th2) cell predominance in these mice, which protected them against the development of cerebral malaria. These mice significantly prolonged their survival, compared with the control mice after P. berghei infection. All of the mice not inoculated with irradiated L3 died within 12 days with acute neurological manifestations unrelated to the level of parasitaemia after infection of P. berghei. Conversely, most of the inoculated mice lived more than 3 weeks following infection with P. berghei, dying in the fourth week of severe anaemia and overwhelming parasitaemia. This suggests that Th2-dominant responses lead to the down-regulation of susceptibility to murine cerebral malaria.

Brugia pahangi : production of a monoclonal antibody reactive with the surface of infective larvae

Monoclonal antibodies against infective third-stage larvae (L3) of Brugia pahangi were generated from mice immunized with L3 antigens. The monoclonal antibodies were L3 stage-specific or stage-nonspecific. A BpG1 monoclonal antibody (IgG1 subclass) showing L3 stage-specificity was examined in detail. BpG1 recognized the surface of B. pahangi L3 and also reacted with the surface of Brugia malayi L3 but not with the surface of filarial worms of other genera, such as Acanthocheilonema viteae and Litomosoides carinii. BpG1 promoted cellular adhesion to the surface of B. pahangi L3. BpG1 bound on living L3 was shed but the shedding rate was relatively slow. The surface antigen recognized by BpG1 had a molecular weight of 58 kDa. It was stable to heat and periodate treatments but sensitive to trypsin digestion and was released from living L3 by SDS but not by Triton X-100 or CTAB. Preincubation of L3 with BpG1 significantly reduced the recovery rate of worms compared with the preincubation with a monoclonal antibody (IgG1 subclass) against the inner tissues of B. pahangi L3 or control supernatant of P3U1 myeloma cells. This result suggests that the antigen containing the BpG1 epitope may be one of the targets of a protective immune response against Brugia infection.

Induction of FcεRII/CD23 on human T cells by excretory and secretory antigen of dirofilaria immitis

We investigated the capacity of excretory and secretory antigen (ES) derived from living filarial worms in the induction of CD23 expression on human peripheral blood T cells by using flow cytometry. ES (10 μg/ml) significantly induced the expression of CD23 on human T cells. Moreover, increased CD23 expression was completely abolished by preincubation with specific antibody to ES. The results suggest that ES might play a certain role in IgE antibody production by induction of CD23 expression on T cells.

Non-specific immune suppression by CD8+ T cells in Brugia pahangi-infected rats.

Non-specific suppression of the immune response was investigated in Brugia pahangi-infected Lewis rats. The proliferative response of peripheral blood lymphocytes or splenic non-adherent cells to mitogens was significantly reduced by B. pahangi infection. The degree of hyporesponsiveness of splenic non-adherent cells to mitogens was comparable between microfilaremic and non-microfilaremic animals. The suppressed proliferative response of splenic non-adherent cells was restored by blocking with anti-CD8 monoclonal antibody. After separation of T cells into CD4+ and CD8+ subpopulations, only CD8+ T cells from B. pahangi-infected rats suppressed the proliferative response of normal spleen cells to concanavalin A. CD8+ T cells from normal rats had no suppressive effect. On the other hand, the proliferative response of CD4+ T cells to concanavalin A was comparable between normal and infected rats. These results suggest that CD8+ T cells participate in the non-specific suppression of immune response in experimental filariasis.

Increased susceptibility of BALB/c mice to infection with Brugia pahangi when treated at an early stage with a single dose of carrageenan or promethazine

Abstract Immunocompetent BALB/c mice are resistant to infection with Brugia pahangi ( B. pahangi ). In mice treated with a single dose of carrageenan (CGN) or promethazine (PMZ) at an early stage of infection, adult worms and microfilariae were recovered at 12 weeks post-inoculation (PI) with third-stage infective larvae (L3); neither was recovered from control mice. To observe local cellular responses in CGN-treated, PMZ-treated and control mice, we investigated the peritoneal cavities on days 4, 8, 12 and 14 PI. In control mice, larvae were encapsulated by peritoneal exudate cells (PEC) from day 4 PI; morphological observations showed the macrophages and eosinophils were involved with rapid and intense cellular reactions to the larvae. The PEC count was significantly lower in CGN-treated than in control mice on days 8 and 12 PI. The eosinophil content in the PEC of the CGN-treated mice was 0% on days 4, 8 and 12 PI and the larvae were not surrounded by PEC, while it was significantly lower in PMZ-treated mice than in control mice on days 8 and 12 PI; larvae were surrounded by PEC from day 8 PI. The rate of recovery of living larvae was significantly higher in CGN-treated or PMZ-treated mice than in control mice on day 14 PI. These results suggest that the resistance of mice to B. pahangi infection may be determined by early-stage cellular reactions to the larvae; blocking the functions of macrophages and/or eosinophils at this stage may increase susceptibility to infection.

Differential susceptibil ity to Brugia pahangi infection in Mongolian gerbils (Meriones unguiculatus) of different coat colour

The influence of intraspecific host variables on the response to parasitic infections is an important aspect of host-parasite relationships, yet little is known about this aspect of filariasis for lack of a model. This study presents coat colour mutants of the Mongolian gerbil (Meriones unguiculatus) as potential new models for research into the effects of host genetic variation on response to filarial infection. Peak level of microfilaraemia, eosinophil response, body weight and degree of splenomegaly in gerbils infected with Brugia pahangi varied with agouti, albino, and black coat colour. These results suggested that coat colour-related genes might influence host immune response to developmental stages of the parasite and eosinophil-mediated reaction might cause host damage.

Antigens responsible for eosinophil hyporesponsiveness in Brugia pahangi microfilariae injected mice

In order to identify the eosinophil hyporesponsiveness factor in the microfilaremic host, stage-specific monoclonal antibodies against microfilariae (Mf) of Brugia pahangi were produced. One of these (MfG2a) was established for the first time as a monoclonal antibody of IgG2a isotype against Mf. MfG2a recognizes the eosinophil hyporesponsiveness factor, the 42 kDa excretory/secretory antigen of Mf. Treatment of MfG2a significantly (P < 0.05) induced eosinophil response with rapid reduction of microfilaremia in previously Mf injected mice which became amicrofilaremic within 2 weeks. Eosinophil hyporesponse was observed in the control microfilaremic mice and the microfilaremia persisted at high levels. Another monoclonal antibody, MfG1 of the IgG1 class, recognized the 64-kDa surface antigen of Mf, MfG1 was less effective in eosinophil response- or microfilaremia reduction. These data suggest that the 42-kDa microfilarial excretory/secretory antigen might be responsible for the eosinophil hyporesponsiveness in B. pahangi Mf injected mice.

Suppression of mitogen-induced IL-2Rα expression in PBL by serum from microfilaraemic rats chronically infected with Brugia pahangi

To study immunological responses in filarial infections, interleukin-2 receptor alpha (IL-2R alpha) expression in the peripheral blood lymphocytes (PBL) of Lewis rats infected with Brugia pahangi was observed by flow cytometry. During infection, no increase in IL-2R alpha was observed in either microfilaraemic or amicrofilaraemic rats. The PBL of rats were stimulated with phytohaemagglutinin (PHA) and the frequency of IL-2R alpha-positivity was examined. After microfilariae appeared, the increase in the rate of IL-2R alpha-positivity in microfilaraemic rats was less than in amicrofilaraemic rats. The anergy of IL-2R alpha expression in microfilaraemic rats was restored when their lymphocytes were cultured with normal rat serum. IL-2R alpha expression in normal uninfected rats decreased when cultured with serum from microfilaraemic rats. These results suggest that microfilariae-related factors in rat serum suppress PHA-induced IL-2R alpha expression in PBL and thus inhibit cell proliferation and host immunity.