IgE antibodies against Trypanosoma cruzi arginine kinase in patients with chronic Chagas disease.

Arginine kinase (AK) is an enzyme present in various invertebrates, as well as in some trypanosomatids such as T. cruzi, the etiological agent that causes Chagas disease. In invertebrates, this protein acts as an allergen inducing an IgE-type humoral immune response. Since AK is a highly conserved protein, we decided to study whether patients with chronic Chagas disease (CCD) produce specific antibodies against T. cruzi AK (TcAK). Plasma from patients with CCD, with and without cardiac alterations and non-infected individuals were evaluated for the presence of anti-TcAK IgG and IgE antibodies by ELISA, including detection of specific IgG subclasses. Our results showed that the levels of specific anti-TcAK IgG and IgE were different between infected and non-infected individuals, but comparable between those with different clinical manifestations. Interestingly, anti-TcAK IgG4 antibodies associated with IgE-mediated allergenic processes were also increased in CCD patients. Finally, we found that several of the predicted B cell epitopes in TcAK matched allergenic peptides previously described for its homologues in other organisms. Our results revealed for the first time a parasite's specific IgE antibody target and suggest that TcAK could contribute to delineate an inefficient B cell response by prompting a bias towards a Th2 profile. These findings also shed light on a potential allergenic response in the context of T. cruzi infection.

Sulfates are main targets of immune responses to cruzipain and are involved in heart damage in BALB/c immunized mice.

Trypanosoma cruzi, the agent of Chagas disease contains a major cysteine proteinase, cruzipain (Cz), with an unusual carboxyl-terminal extension (C-T). We have previously reported the presence of sulfate groups in the N-linked oligosaccharide chains of this domain. In order to evaluate the immune responses to sulfated moieties on Cz, BALB/c mice were immunized with purified Cz and C-T prior and after desulfation treatment. The humoral immune response to sulfates on Cz or C-T was mainly IgG2b. Interestingly, the abolishment of IgG2b reactivity when desulfated antigens were used as immunogens demonstrates that esterified sulfate groups are absolutely required for eliciting IgG2b response to Cz. Sera from chronically T. cruzi-infected subjects with mild disease displayed higher levels of total IgG and IgG2 antibodies specific for sulfated epitopes compared with those in more severe forms of the disease. A significant reduction of C-T-specific delayed-type hypersensitivity reaction in C-T-immunized mice was observed when desulfated C-T was challenged, suggesting the involvement of sulfate groups in the generation of memory T-cell responses. Moreover, immunization with C-T in the absence of infection elicited ultrastructural abnormalities in heart tissue. Surprisingly, hearts from sulfate-depleted C-T-immunized mice did not present pathological alterations. This is the first report showing that sulfate-bearing glycoproteins from trypanosomatids are able to elicit specific humoral and cellular immune responses and appeared to be involved in the generation of heart tissue damage. These results represent a further step in the understanding of the role of Cz in the course of T. cruzi infection.