A high-resolution radiation hybrid map of the human genome draft sequence.

We have constructed a physical map of the human genome by using a panel of 90 whole-genome radiation hybrids (the TNG panel) in conjunction with 40,322 sequence-tagged sites (STSs) derived from random genomic sequences as well as expressed sequences. Of 36,678 STSs on the TNG radiation hybrid map, only 3604 (9.8%) were absent from the unassembled draft sequence of the human genome. Of 20,030 STSs ordered on the TNG map as well as the assembled human genome draft sequence and the Celera assembled human genome sequence, 36% of the STSs had a discrepant order between the working draft sequence and the Celera sequence. The TNG map order was identical to one of the two sequence orders in 60% of these discrepant cases.

Antimicrobial susceptibility patterns and high-level gentamicin resistance among enterococci isolated in a Mexican tertiary care center.

AIM: To describe the antimicrobial susceptibility pattern of enterococcal clinical isolates. SETTING: A 200-bed tertiary-care center in Mexico City. STUDY DESIGN: Prospective surveillance of enterococcal clinical isolates identified according to Facklam's method since 1990. Susceptibility tests were performed by a commercial micromethod, agar diffusion and microbroth dilution. We present data from 1990 to 1992. RESULTS: A total of 407 enterococci were recovered during the study period: 245 from inpatients and 162 from outpatients; 325 of the isolates were Enterococcus faecalis, 61 E. faecium, seven E. avium, four each for E. raffinosus and, E. hirae; two, E. pseudoavium; and one each E. gallinarum, E. durans; E. mundtii, and E. faecales var asacharolyticus. Resistance to ampicillin and imipenem among E. faecium was 59%. Among E. faecalis, 0.3% were resistant to ampicillin and 2% to imipenem; no beta-lactamase production was detected. All were susceptible to vancomycin. Overall, a 12% high-level gentamicin resistance (HLGR) was found without a difference between species; 25% of bloodstream clinical isolates were HLGR enterococci. More than half (63%) of the HLGR clinical isolates were susceptible to streptomycin; a-hemolysis in human blood agar as well as nitrofurantoin resistance were observed in all E. faecium isolates and in two E. avium. CONCLUSIONS: In our center, HLGR has a prevalence of 12%. Streptomycin may be a therapeutic alternative in 63% of the HLGR cases. The pattern of hemolysis in human blood agar plus the susceptibility to nitrofurantoin could be used as an initial screening to identify enterococci.

HLA-DR4 (DRB1*0401) transgenic mice expressing an altered CD4-binding site: specificity and magnitude of DR4-restricted T cell response.

Optimum function of HLA-DR molecules in transgenic mice requires efficient interaction between the class II molecules on APCs and CD4 on T cells. Residues 110 and 139 of the second domain of class II molecules are considered to be critical for recognition of CD4. We generated an HLA-DR4beta(NT) transgene construct in which positions 110 and 139 were altered to resemble endogenous mouse H2 Abeta molecules. This construct was introduced into (B10 x SWR) embryos, and DR4beta(NT) transgenic mice were produced. The transgene was transferred into B10.RFB3 (Ebeta0 EalphaP) mice. The transgene-encoded DR4beta molecules paired with endogenous Ealpha chains to form stable DR4beta/Ealpha dimers expressed on the cell surface. The hybrid dimers showed similar Ag-binding specificity to HLA-DR4 molecules and positively selected CD4+ T cells in vivo. Immunization of HLA-DR4beta(NT) transgenic mice with DR4-restricted peptides induced T cell proliferation in vitro. While the purified T cells from DR4beta(NT) transgenic mice responded strongly to the HA(307-319) presented by M12C3 transfectants expressing altered DR4beta/Ealpha heterodimers, the response to the same peptides presented by transfectants expressing wild-type DR4beta/Ealpha molecules was substantially reduced. Taken together, these data confirmed in vitro studies on the importance of these residues in CD4-MHC class II interaction. The altered HLA-DR4beta transgenic mice were able to overcome the species barrier and generate efficient HLA-DR4-restricted CD4-specific immune responses. Thus, residues 110 and 139 were critical for the interaction of class II with CD4 T cells during thymic selection as well as peripheral immune responses.