Ir gene regulation of T cell proliferation: requirement for Ia and antigen expression on the same accessory cell

These results demonstrate that only splenic macrophages expressing both Ir products (function) and the antigen (GAT) were able to reconstitute the T cell response of cultures in which the splenic macrophage monolayer had been treated with appropriate anti I-A antibodies. This inhibition was not a result of induced suppression caused by anti-Ia treatment but rather a masking of Ia antigen which prevents the T cell receptor(s) from recognizing either the Ir gene product and specific antigen in complex or separately.

Liposarcoma of the lower extremity

Twenty patients with primary liposarcoma of the lower extremity were treated over a 25-year period. The adequacy of the initial surgical procedure and histological grade of malignancy both influenced survival rates. In addition local recurrence was noted only in patients who had undergone "inadequate" initial excision. Inguinal lymph nodes were uninvolved by tumor in all cases. In general, patients with liposarcomas of myxoid and/or round cell type survived for long periods of time. However, even patients with myxoid lesions occasionally exhibited evidence of early blood-borne metastases. This study suggests an important relationship between an inadequate primary resection, local recurrence, and eventual retroperitoneal spread. In the majority of cases, this may have resulted from failure to control the primary distal extremity tumor, with subsequent contiguous spread of metastases into the ipsilateral retroperitoneal space. If feasible, radical soft part resection should be performed as the primary surgical therapy of these neoplasms. Tumors contiguous to the knee or ankle joint should be treated by primary amputation. Failure to control local disease may result in blood-borne dissemination or local spread along musculoaponeurotic planes to involve proximal groin or retroperitoneal space.

Association of chromosome loss with centromere-adjacent mitotic recombination in a yeast disomic haploid

Experiments designed to characterize the association between disomic chromosome loss and centromere-adjacent mitotic recombination were performed. Mitotic gene convertants were selected at two heteroallelic sites on the left arm of disomic chromosome III and tested for coincident chromosome loss. The principal results are: (1) Disomic chromosome loss is markedly enhanced (nearly 40-fold) over basal levels among mitotic gene convertants selected to arise close to the centromere; no such enhancement is observed among convertants selected to arise relatively far from the centromere. (2) Chromosome loss is primarily associated with proximal allele conversion at the centromere-adjacent site, and many of these convertants are reciprocally recombined in the adjacent proximal interval. (3) Partial aneuploid exceptions provisionally identified as carrying left arm telocentrics have been found. A testable model is proposed suggesting that centromere involvement in genetic recombination may precipitate segregational disfunction leading to mitotic chromosome loss.

Cytomegalovirus-associated gastric ulcer

A patients with a cytomegalovirus (CMV) post-transfusion syndrome developed upper gastrointestinal tract bleeding; subsequently, a gastric ulcer was found. CMV was searched for in the gastroscopic biopsy material because the gastric ulcer had occurred in a setting of CMV mononucleosis. CMV cells were found in gastroscopic biopsy sections and CMV was also cultured from biopsy material. This study illustrates the feasibility of antemortem diagnosis of CMV-associated disease of the upper gastrointestinal tract.

Immunosuppressive activity of a subline of the mouse EL-4 lymphoma. Evidence for minute virus of mice causing the inhibition

Filtered culture fluids from the early in vitro passages of a subline of the C57BL/6 mouse EL-4 lymphoma, EL-4(G-), were strongly inhibitory for BABL/c vs. C57BL/6 mixed lymphocyte cultures (MLC). The inhibitory activity could be preserved by storage at -75 degrees C or 4 degrees C, thus allowing its further characterization. The inhibitory factor was particulate (nondialyzable, sedimentable at 100,000 g for 1 h), very small (recovered after 0.10 mum filtration), sensitive to UV irradiation, but heat stable (56 degrees C, 1 h) and resistant to chloroform. It was infectious, since later, noninhibitory passages of EL-4(G-) tissue culture cells became strongly inhibitory upon inoculation with the culture fluid. This data was consistent with the inhibitory factor being an infectious virus. Virus analysis by mouse antibody production tests revealed that viruses were indeed present in EL-4(G-) ascites cells and in the culture fluid, and not in a late passage of EL-4(G-) tissue culture cells which were not inhibitory. Neutralization of the inhibitory factor was achieved by pretreatment with ascitic fluid or with the sera raised against those (EL-4(G-)-derived materials which contained viruses. Mouse reference immune sera against minute virus of mice (MVM) completely neutralized the inhibitory factor in the culture fluid or in EL-4(G-) ascites cells. Two prototype MVM strains, and one Kilham rat virus preparation, did not inhibit the mouse MLC. Thus, the possibility exists that a variant of MVM, or an unidentified virus, has been grown and selected for in EL-4(G-) cells and recognized, due to its immunosuppressive characteristics. In any event, immunosuppression by EL-4(G-) cells was not mediated by the tumor cells, their metabolic products, or associated endogenous type C viruses, but by an exogenous virus, most likely a variant MVM with immunosuppressive characteristics. This adds weight to a parallel observation from our laboratory on the immunosuppressive effects of Kilham rat virus in rat lymphocyte cultures.

Mitotic chromosome loss in a disomic haploid of Saccharomyces cerevisiae

Experiments designed to characterize the incidence of mitotic chromosome loss in a yeast disomic haploid were performed; The selective methods employed utulize the non-mating property of strains disomic for linkage group III and heterozygous at the mating type locus. The principal findings are: (1) The grequency of spontaneous chromosome loss in the disome is of the order 10- minus 4 per cell; this value approximates the frequency in the same population of spontaneous mitotic exchange resulting in homozygosity at the mating type locus. (2) The recovered diploids are pure clones, and thus represent unique events in the disomic haploid. (3) Of the euploid chromosomes recovered after events leading to chromosome loss, approximately 90% retain the parental marker configuration expected from segregation alone; however, the remainder are recombinant for marker genes, and are the result of mitotic exchanges in the disome, especially in regions near the centromere. The recombinant proportion significantly exceeds that expected if chromosome loss and mitotic exchange in the disome were independent events. The data are consistent with a model proposing mitotic nondisjunction as the event responsible for chromosome loss in the disomic haploid.

Kinetics of the mating-specific aggregation in Saccharomyces cerevisiae

Procedures are described for obtaining efficient mating (zygote formation) in the heterothallic yeast Saccharomyces cerevisiae. The methods separate operationally the initial, mating-specific aggregation from subsequent steps in conjugation. This cell-cell interaction has been characterized. The data support the conclusions that (i) aggregation in liquid suspension is a random collision process, and (ii) only non-budded cells participate in aggregation. A mathematical model for the kinetics of aggregation in liquid suspension has been developed which is in good agreement with the experimental data.

THE INDUCTION OF MITOTIC GENE CONVERSION BY X-IRRADIATION OF HAPLOID SACCHAROMYCES CEREVISIAE

Mitotic recombination in Saccharomyces cerevisiae was examined by means of experiments in which one of the haploid parents was X-irradiated prior to zygote formation. By this method radiation-induced lesions are restricted to only one of the two non-sister chromatids that may be expected to undergo mitotic exchange in the diploid. The principal results of this work are: (1) X-irradiated haploid cells that are incapable of further vegetative growth (colony formation) are efficiently rescued into viable diploids by mating with unirradiated haploid cells. (2) X-rays delivered to only one of the two haploid parents are recombinogenic in the resultant diploid. The frequency of detected recombinational events increases as a probable linear function of the X-ray dose. (3) A majority of the induced recombinational events are nonreciprocal in nature (mitotic gene conversion). These results complement those obtained from X-irradiation of the vegetative diploid itself, where the induced genetic exchanges are principally reciprocal.