When termination codons were introduced into exons of the gene for Ig mu chain, steady-state levels of mu mRNA were reduced, both at the pre-B cell stage and at the plasma cell stage. A termination codon in the variable region gene segment and a termination codon in the second exon of the constant region gene segment had effects of similar magnitude. When the termination codon was deleted, the original level of mRNA was restored. The rate of mu gene transcription was the same whether or not a termination codon was present. Therefore, the termination codons must reduce the amount of the mRNA by reducing its stability. Since the introduced termination codons prematurely terminate translation and, in so doing, change the ribosome load on the mRNA, we conclude that mu mRNA stability is conferred in part by ribosomal protection from enzymatic degradation. We propose that the differences in mu mRNA stability during B lymphocyte differentiation are due to different amounts of ribosomes available for translation.

Although AIDS patients lose human immunodeficiency virus (HIV)-specific cytotoxic T cells, their remaining CD8-positive T lymphocytes maintain cytotoxic function. To exploit this fact we have constructed bispecific antibodies that direct cytotoxic T lymphocytes of any specificity to cells that express gpl20 of HIV. These bispecific antibodies comprise one heavy/light chain pair from an antibody to CD3, linked to a heavy chain whose variable region has been replaced with sequences from CD4 plus a second light chain. CD3 is part of the antigen receptor on T cells and is responsible for signal transduction. In the presence of these bispecific antibodies, T cells of irrelevant specificity effectively lyse HIV-infected cells in vitro.

In 1979-1980, a distinct outbreak of hepatitis A occurred among homosexual men in Stockholm, Sweden, city and county area. The epidemic comprised 145 known cases. It began in December 1979 and progressed in waves during the following 10 months, with three distinct peaks separated by about six-week intervals. Actually, the incidence of hepatitis A in the Stockholm area showed a fivefold increase during 1980 as compared to the previous year. Clinical serologic, and social characteristics were studied more closely in 98 of the 145 homosexual men. Verification of hepatitis A was made by a solid-phase radioimmunoassay technique for detection of antibody to hepatitis A virus of the immunoglobulin M class. In addition, 64% of the men showed findings consistent with a prior hepatitis B (antibody to hepatitis B core antigen and/or antibody to hepatitis B surface antigen) and 34% were Treponema pallidum immobilization-positive from a prior or concomitant syphilis. Employment in risk professionals was common; thus, 19% worked in restaurants or otherwise handled food and 20% were engaged in medical care as compared to the 1% occupied in either branch of work among the general population in Sweden. Sexual habits with multiple partners and oral-anal sexual contacts were judged to be of major importance in the spread of this epidemic. Some spread of hepatitis A to the general population probably occurred due to the risk occupations of many homosexual men.

Immunoglobulin genes are generated during differentiation attempted at the c locus, and that only upon failure to produce a functional n: chain is there an attempt to rearrange the ;t locus; and (b) the stochastic theory, which postulates that rearrangement at the , locus proceeds at a rate that is intrinsically much slower than that at the c locus. We show here that ;-chain genes are generated whether or not the c locus has lost its germ-line arrangement, a result that is compatible only with the stochastic theory.

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