HUMAN T-CELL RESPONSES AGAINST THE MAJOR CYSTEINE PROTEINASE (CRUZIPAIN) OF TRYPANOSOMA-CRUZI - ROLE OF THE MULTIFUNCTIONAL ALPHA(2)-MACROGLOBULIN RECEPTOR IN ANTIGEN PRESENTATION BY MONOCYTES

Chagas' disease patients (CDP) develop both humoral and cellular immun e responses against the major cysteine proteinase (cruzipain) from Try panosoma cruzi. Here we demonstrate that complexes formed by cruzipain and alpha(2)-macroglobulin (alpha(2)M) are efficiently internalized b y human monocytes, and that this process results in enhanced presentat ion of cruzipain peptides to CD4(+) T cells from CDP. Purified or seru m alpha(2)M binds to polymorphic cruzipains, but only a fraction of th e proteinases become covalently linked. Once bound to alpha(2)M, fluor escein-labeled cruzipain (FITC-cruzipain) or [I-125]cruzipain were mor e efficiently internalized by normal peripheral blood mononuclear cell s (PBMC) or monocytes; this effect was abolished by (i) pre-treating t he cells with receptor-associated protein (rRAP), a known antagonist t he of alpha(2)M receptor (alpha(2)MR/LRP), and (ii) inactivating [I-12 5]cruzipain's active site prior to the reaction with alpha(2)M, indica ting that the exposure of receptor binding sites on alpha(2)M complexe s required bait region cleavage, We then sought to determine if the al pha(2)MR/LRP-dependent uptake of alpha(2)M:cruzipain by monocytes resu lted in increased CD4(+) T cell responses of PBMC-CDP (n = 13). These effects were only revealed after depletion of CD19(+) B lymphocytes fr om PBMC-CDP; the threshold of T cell stimulation was far lower in cult ures stimulated with alpha(2)M:cruzipain, as compared to antigen alone . Myocardial specimens from CDP with chronic myocardiopathy (three nec ropsies) were analyzed by immunohistochemistry with mAb anti-cruzipain or anti-alpha(2)M/LRP (CD91(+)). Extracellular depots of cruzipain we re localized amidst inflammatory mononuclear infiltrates, part of whic h contained CD91(+) macrophage-like cells. Ongoing studies should clar ify if T. cruzi cysteinyl proteinases play a role in the pathogenesis of Chagas' heart disease.