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We have studied the maturation of the immune response by looking at the generation of antibody diversity in germinal centre B cells. Mice were immunized with the antigen 2-phenyloxazolone. Germinal centre B cells, defined by their strong binding to peanut agglutinin (PNA(hi], were sorted from the spleen and fused. Ten days after immunization high numbers of antigen specific hybridoma lines were obtained from the PNA(hi) subset of B cells, suggesting that the small fraction of B cells which are PNA(hi) harbour the antigen activated population. The majority of the day 10 sequences from PNA(hi) cells were shown to be mutated. However, in contrast to results from later stages of the immune response, most of the mutations found were silent. The preferential expansion of B cell clones expressing the mutations characteristic of the mature response was not observed at this stage. Among these hybridoma lines was at least one which, apparently through somatic mutation, had lost the ability to bind antigen. We conclude that in the micro-environment of the germinal centre the B cell repertoire is diversified by hypermutation.

The effects of a new policy limiting smoking to separate, designated areas in School of Education buildings at the University of Köln, Germany, were analyzed. Although the majority (77%) of the 1,223 students surveyed did not expect the changed policy to affect their smoking habits, approximately 28% of the men and 30% of the women said they were smoking less at the university after the change went into effect. Ninety-one percent of the nonsmoking students and 68% of the smokers supported the new policy. Smoking rates among Köln students are not significantly different from those of the adult German population, where 34% of the women and 41% of the men are smokers. The findings in this study indicate that such a policy change may result in a net decrease in amount smoked and could be a successful intervention in countries where smoking rates are traditionally higher than they are in the United States.

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