Trehalose-containing lipooligosaccharide antigens of Mycobacterium sp.: presence of a mono-O-methyltri-O-acyltrehalose "core".

We have described the surface antigens of Mycobacterium kansasii as trehalose-containing lipooligosaccharides (LOS) which at the nonreducing "epitope" end bear a unique amino sugar containing diglycosyl unit, whereas the putative reducing end consists of an acylated alpha, alpha-trehalose-containing tetraglucosyl "core" [Hunter, S. W., Jardine, I., Yanagihara, D. L., & Brennan, P. J. (1985) Biochemistry 24, 2798-2805]. The presence of a new variation on this core, in Mycobacterium szulgai, is now reported, ----3)beta-D-Glcp-(1----6)alpha-D-Glcp(1----1)3,4,6-tri-O-acyl-2-O- Me-alpha-D-Glcp, representing the first example of an O-methyltrehalose unit in nature. The simplest of the LOS class of glycolipids in M. szulgai was defined as alpha-L-2-O-Me-Fucp(1----3)alpha-L-Rhap(1----3)alpha-L-Rh ap(1----3) beta-D-Glcp(1----6)alpha-D-Glcp(1----1)3,4,6-tri-O-acyl-2-O-Me-alpha-D-G lcp. Further glycosylation of this nonantigen, by an incompletely defined 6-deoxyhexosyl residue, confers specific antigenicity on the organism. Thus, these extraordinary structures, in a manner analogous to the better known lipopolysaccharides from rough variants of Enterobactericiae, are highly amphipathic and display variability not only in the immunogenic, distal region but also in the "invariant" lipophilic core. The contribution of these glycolipids to the hydrophobic barrier, the pseudo outer membrane of mycobacteria, is discussed.

A large deletion within the T-cell receptor beta-chain gene complex in New Zealand white mice.

The T-cell receptor beta-chain gene complex contains a duplication of D beta, J beta, and C beta gene segments in mice and man. When DNA from many inbred strains of mice was screened an unusual allele of the beta locus was identified in New Zealand White (NZW) mice. This allele is distinguished by the deletion of an 8.8-kilobase segment of DNA containing C beta 1, D beta 2 and the J beta 2 cluster. Despite the fact that all NZW T-cell receptors must be derived from a single set of beta-chain gene segments, this strain has functional T cells and is phenotypically normal. This deletion of T-cell receptor beta-chain segments occurs in a strain known to contribute to lupus-like autoimmune disease.

Perceptions of freshman medical students of gender differences in medical specialty choice.

At present, it is not clear whether or not the choices of specialty areas by male and female medical students are converging. Historically, women have selected specialty areas with high patient contact. In the study reported here, the authors address whether or not there are differences in perceived specialty choice among the newest entrants into medicine. A total of 180 freshman medical students at one medical school (120 males and 60 females) participated. It was found that 70.4 percent of the women stated that they expected to select a specialty in primary care compared with only 44.4 percent of the men. On the other hand, 30.8 percent of the men expected to enter a surgical specialty area compared with only 11.1 percent of the women. A higher proportion of women than of men indicated that patient contact and family life were instrumental in the selection of a medical specialty. Seventy percent of the men expected an annual income of more than +75,000 (in 1984 dollars) compared with 43.3 percent of the women, who generally expected a smaller income. The authors in this study found that the traditional identifications of both male and female specialty choices are not changing.

Enzyme-linked immunosorbent assay of glycolipid antigens for identification of mycobacteria.

Enzyme-linked immunosorbent assays which are based on species- or type-specific glycolipids antigens and in which rabbit antisera are prepared with homologous strains are capable of distinguishing among serological variants of the Mycobacterium avium-Mycobacterium intracellulare-Mycobacterium scrofulaceum complex, Mycobacterium chelonei subspecies chelonei and abscessus, Mycobacterium simiae I and II, Mycobacterium kansasii, Mycobacterium szulgai, Mycobacterium xenopi, and Mycobacterium fortuitum biovariant peregrinum. The immunoreactive glycolipids can be divided into two classes. Those resistant to alkali, the C-mycoside glycopeptidolipids, are present in the M. avium-M. intracellulare-M. scrofulaceum, the M. chelonei subspecies chelonei and abscessus, and the M. simiae I and II complexes and in M. fortuitum biovariant peregrinum. The alkali-labile glycolipid antigens, the lipooligosaccharides, are present in M. kansasii, M. szulgai, and M. xenopi. In one study, the combination of enzyme-linked immunosorbent assay and alkaline susceptibility was compared with seroagglutination in the identification of 60 clinical isolates of nontuberculous mycobacteria: 45 showed perfect concordance, 9 could be narrowed to one, two, or three possibilities, and the rest did not correspond. In a second study involving 43 clinical isolates that were untypable by seroagglutination or were autoagglutinable, the results of enzyme-linked immunosorbent assay and thin-layer chromatography of glycolipid antigens were compared: 21 showed clear concordance. The results demonstrate that enzyme-linked immunosorbent assay is particularly useful in assessing the antigenicity of lipids, and sensitivity, ease, and rapidity recommend it as an adjunct to seroagglutination and thin-layer chromatography for the identification of nontuberculous mycobacteria.