Enhancement of natural antibodies in mice immunized with exoantigens of pI 4.5 from Trypanosoma cruzi

Selection during development of VH11+ B cells: a model for natural autoantibody-producing CD5+ B cells

Natural autoantibodies constitute a large portion of serum immunoglobulin M (IgM) and bridge the adaptive and innate immune systems, serving as a rapid response to common pathogens. Many arise from a distinctive subset of B cells, termed B-1, that express CD5. Here, we describe our studies with a representative CD5+ B-cell-derived natural autoantibody, the VH11Vkappa9 B-cell receptor (BCR) that binds a determinant on senescent erythrocytes. This specificity represents 5-10% of the CD5+ B-cell subset, with a large portion accounted for by two novel BCRs, VH11Vkappa9 and VH12Vkappa4. We have found that the development of B-lineage cells with a VH11 rearrangement is surprisingly restricted at several crucial bottlenecks: (i). one of the most common VH11 rearrangements generates a heavy-chain protein that only inefficiently assembles a pre-BCR, key for recombinase-activating gene downregulation/allelic exclusion and pre-B-clonal expansion; (ii). cells containing VH11- micro chains lacking N-addition are favored for progression to the B-cell stage, eliminating most bone marrow VH11 rearrangements; and (iii). only a subset of Vkappa-light chains combine with VH11 heavy chain to foster progression to the mature B-cell stage. Together, these constrain VH11 generation to fetal development and may favor production of B cells with the prototype VH11Vkappa9 BCR.

Frequency of antinuclear antibodies in healthy children and adolescents

Sera from 214 healthy children and adolescents (108 females [50.4%]) aged 6 months to 20 years (mean 8.7 years) and from 116 patients with rheumatic diseases were assayed for antinuclear antibody (ANA) by indirect immunofluorescence (IIF) by using HEp-2 cells as substrate. Twenty-seven healthy children (12.6%) presented a positive ANA test; there was no difference between genders, and we observed a trend for higher frequency of ANA >/= 1/80 among children between 5 years and 10 years. Eight of the 27 healthy children with positive ANA test were reevaluated 36 months later, and none of them had developed any rheumatic disease, though the sera remained positive in 2 of them. ANA was present in 42/116 patients (36.2%). In daily medical practice ANA determination should be required only in individuals with clinical signs and symptoms suggestive of autoimmune disease.

Partial protection of mice against Trypanosoma cruzi after immunizing with the TcY 72 antigenic preparation

A 72 kDa Trypanosoma cruzi glycoprotein recognized by the 164C11 monoclonal antibody (IgM isotype) was purified by preparative electrophoresis. The antigenic preparation obtained, named TcY 72, was used to immunize C57Bl/10 mice. The following results were observed after immunization: (1) induction of higher titres of IgG than IgM antibodies, as evaluated by indirect immunofluorescence; (2) significant DTH after injection of epimastigotes in mice footpads; (3) peak parasitemia in immunized mice was significantly reduced and animals were negative by 13 days post-infection, although the mice still succumb to infection; (4) the phenotypic analysis of spleen cell populations showed a decrease in the CD4/CD8 ratio in immunized mice. Taken as a whole, these findings indicate that TcY 72 is immunogenic and potentially important for protective immunity.

Exoantigens from trypanosoma cruzi contain cruzipain

This paper shows that human antibodies specific for exoantigens of pI 4.5 (Eas 4.5), released by the blood forms of the parasite, obtained from chagasic patients sera by immunoabsorption react with cruzipain, the major cysteinyl proteinase of Trypanosoma cruzi. Sera from mice immunized with Eas 4.5 also recognize cruzipain. In addition, mouse antisera to cruzipain were reactive with Eas 4.5 as well as with total antigens excreted by culture-trypomastigotes. This reactivity was inhibited by cruzipain as revealed by enzyme-linked immunosorbent assay (ELISA). Furthermore, it was observed by immunoblot that the exoantigens recognized by mouse antisera to cruzipain have molecular weights between 50 and 60 kDa and human antibodies specific for Eas 4.5 recognize cruzipain with apparent molecular weight of 50 kDa. These findings suggest the presence of cruzipain in Eas and the subsequent release of this enzyme by the parasite.

Natural autoantibodies

Autoantibodies of the IgM, IgG and IgA classes, reactive with a variety of serum proteins, cell surface structures and intracellular structures, are 'naturally' found in all normal individuals. Present in human cord blood and in 'antigen-free' mice, their variable-region repertoire is selected by antigenic structures in the body and remains conserved throughout life. Encoded by germline genes with no, or few, mutations, natural autoantibodies are characteristically 'multireactive' and do not undergo affinity maturation in normal individuals. Natural autoantibodies may participate in a variety of physiological activities, from immune regulation, homeostasis and repertoire selection, to resistance to infections, transport and functional modulation of biologically active molecules.