Usefulness of IS6110-restriction fragment length polymorphism typing of Brazilian strains of Mycobacterium tuberculosis and comparison with an international fingerprint database.

Strains of Mycobacterium tuberculosis isolated from 219 different tuberculosis patients, 115 from patients residing in Rio de Janeiro, 79 from Rio Grande do Sul and the remaining from other regions of the country, were analyzed by IS6110-restriction fragment length polymorphism fingerprinting. The IS6110-DNA patterns from these strains were highly polymorphic: 174 different patterns were observed and 25 patterns were shared by 70 isolates (32%). Most strains (93.4%) had multicopy patterns and only 17% of clustered strains had less than six IS6110 copies. Strain clustering was significantly higher for isolates from Rio Grande do Sul (36.7%) in comparison with strains from Rio de Janeiro (22.6%), but only when using high stringency during cluster analysis. Upon screening of an international database containing 3,970 fingerprints of M. tuberculosis strains, 15% of the patterns of Brazilian strains (21% of the strains) were identical to a fingerprint of an isolate from another country and one particular eight-band pattern forming the largest Brazilian cluster was detected in seven additional countries, suggesting that international transmission of tuberculosis from and to Brazil could be occurring frequently. Alternatively,preferential use of certain IS6110 integration sites could also be important in high-copy number strains, having important consequences for the use of databases for epidemiological studies on a large scale.

Reconstitution of germinal center formation in nude mice with Th1 and Th2 clones.

We investigated the ability of hemocyanin (KLH)-specific cloned CD4+ T cells expressing defined cytokine profiles to support germinal center (GC) formation in syngeneic athymic recipients in response to hapten-KLH challenge. Th1 clones producing IL-2 and IFN-gamma did not by themselves increase GC production above background, while Th2 cells producing IL-4 and IL-5 did. However, the combination of Th1 and Th2 cytokines was more effective than Th2 cytokines alone, suggesting a synergistic effect in this aspect of their help for B cells. In contrast to GC formation, antibody production could be induced with Th1 or Th2 clones given separately (Th1 clones inducing IgG2a, and Th2 clones inducing IgG1 and IgE). These results indicate that the T cell requirements for GC production are different from those for isotype switching and Ig secretion. It is postulated that the synergy between Th1 and Th2 cells in the induction of GC formation reflects the synergy between Th1 and Th2 cytokines, such as IFN-gamma and IL-5, in promotion of GC cell proliferation.