A gene required for class II-restricted antigen presentation maps to the major histocompatibility complex.

We have previously described a set of mutants (16.23-selected mutants) of a B lymphoblastoid cell line that are defective in the presentation of intact proteins to class II-restricted T cells, but effectively present immunogenic peptides. The mutations in these mutants are recessive in somatic cell hybrids and are not in Class II structural genes. Here, we report on a unique mutant, 5.2.4, in which a similar defect in class II-restricted antigen presentation has occurred in association with a one-megabase homozygous deletion in the class II region of the major histocompatibility complex (MHC). The defects in class II presentation among three of the 16.23-selected mutants, and between these mutants and 5.2.4, are noncomplementary in somatic cell hybrids. This suggests that the class II presentation-defective phenotype in all four mutants results from lesions in a single MHC-linked gene, a conclusion strengthened by the finding that in a hybrid made with a second, unrelated MHC deletion mutant, T2, the class II presentation defect in a 16.23-selected mutant is also not complemented. Mutant 5.2.4, in addition to its class II presentation defect, is also defective in surface expression of MHC class I molecules, most likely because its deletion encompasses the peptide supply factor 1 gene, whose function is known to be required for normal abundance of cell surface class I molecules. However, the surface abundance of class I molecules is normal in the 16.23-selected mutants, suggesting that the lesions affecting class I surface abundance and class II presentation result from mutations in different genes.

Anomalous origin of the left main coronary artery from the right aortic sinus of Valsalva with vasospastic angina.

A case of anomalous origin of the left main trunk of the coronary artery from the right aortic sinus of Valsalva with vasospastic angina is described. Vasospasm was induced in the left main coronary artery by intracoronary administration of ergonovine. To our knowledge, this is the first reported case of vasospastic angina occurring in the presence of the anomalous origin of the left main coronary artery from the right aortic sinus.

Modifying cerebral candidiasis by altering the infectious entry route.

Diffuse leptomeningitis did not occur in healthy adult male Wistar rats with transient candidemia produced by the injection of organisms into the internal carotid artery, even though intraparenchymal microabscesses with yeasts and pseudohyphae were seen throughout the brain. Candida albicans was culturally identified in the brain and kidney. Injecting the organisms into the cisterna magna caused an infection characterized by lymphocytes and histiocytes and was confined to the leptomeninges. In this meningeal model, fungi were recovered only from the CNS. The overwhelming prevalence at autopsy of cerebral candidal microabscesses without diffuse leptomeningitis is apparently due to transient candidemia. Meningitis due to candidemia is rare and seems to require a microabscess that is accessible to the circulating CSF. This latter event is a late and overwhelming feature of cerebral candidiasis.

Exogenously provided peptides fail to complex with intracellular class II molecules for presentation by antigen-presenting cells.

Exogenously supplied antigenic peptides can bind to and be presented by cell surface class II molecules of APCs without prior processing. However, it has been unclear whether peptide Ags exogenously supplied to APCs can also form complexes with nascent intracellular class II molecules that contribute to Ag presentation. We found that exogenously provided peptide Ags, unlike whole protein Ags, are presented as efficiently by fixed as by unfixed B lymphoblastoid APCs, suggesting that intracellular processes do not contribute to the presentation of exogenously supplied peptides by unfixed APCs. Consistent with this finding, exogenously provided peptides do not bind detectably to nascent intracellular class II molecules. We studied the basis for this failure. First, as compared with whole proteins, exogenously supplied peptides accumulate very poorly intracellularly. Second, peptides are more rapidly exocytosed. The limited ability of APCs to accumulate exogenously supplied peptides intracellularly provides a likely explanation for the failure of these peptides to associate with nascent intracellular class II molecules. Exogenously supplied peptides probably never reach the intracellular vesicles in which peptide loading of class II molecules occurs. These findings have implications for the use of peptides therapeutically to block presentation of autoantigens in autoimmune disease.

Quantitation of Candida albicans polysaccharide using an enzyme-linked immunosorbent assay.

The enzyme-linked immunosorbent assay (ELISA) for candida polysaccharide antigen in serum was developed by using double antibody sandwich technique. It was found that serum constituents substantially interfered with the assay. The interference was successfully decreased by heating serum in the presence of EDTA which precipitated interfering serum protein. In addition, candida antigen may be liberated from antibody complexes. The candida polysaccharide antigen in the supernatant was precipitated with ethanol and resuspended in the buffer containing gelatin. A maximum sensitivity of 10 ng/ml was found in the assay using this procedure. This procedure of serum treatment may have potential applications for the detection of other polysaccharide antigens in serum.

Invariant-cognate peptide exchange restores class II dimer stability in HLA-DM mutants.

Class II presentation mutants have mutations in the HLA-DMA or B genes and are defective in the presentation of whole exogenous Ags restricted by HLA-DR, -DQ, and -DP. The functional defect in Ag presentation is accompanied by an altered conformation of cell surface class II molecules and instability of extracted class II dimers in SDS-PAGE; the latter can be corrected by incubation of mutant cells in an acidic pH in the presence of cognate peptide. Here we investigated the basis for correction of class II dimer instability by acid/cognate peptide treatment and the extent to which this treatment corrects the class II conformational defect in DMB mutants. We found that an acidic pH generates peptide binding sites in class II molecules of DMB mutants by eluting invariant chain (li)-derived peptides from them. Cognate peptides can then bind to the empty binding sites of class II molecules in a pH-independent manner, which results in stabilization of class II dimers. Acid/peptide treatment also restores the DR polymorphic epitope recognized by mAb 7.3.19.1 but not the DR polymorphic epitope recognized by mAb 16.23; low pH gradually destroys the 16.23 epitope in nonmutant cells. Mutant 10.24.6, which has a mutation in the DRA coding region creating an extra glycosylation site, also has unstable DR dimers whose stability is restored by acid/peptide treatment. These results suggest that the primary phenotypic defect in both the DMB and 10.24.6 mutants is the abundance of li peptides and lack of cognate peptides bound to class II molecules.

Light-dependent activity of the antitumor antibiotics ravidomycin and desacetylravidomycin.

The antitumor antibiotics ravidomycin and desacetylravidomycin were studied by the biochemical lambda prophage induction assay. In this assay, induction of the enzyme beta-galactosidase is measured as a specific indication of the ability of an agent to directly or indirectly damage DNA. Induction was observed only when these two antibiotics were irradiated with light in the presence of the indicator organism. Drug treated with light followed by incubation with the indicator organism in the dark did not cause induction. Light in both the near UV and visible wave length ranges activated these antibiotics; near UV and visible blue wavelengths were most effective, while 597-nm light was totally ineffective. The amount of induction caused by these drugs varied directly with the dosage of light provided. Bacterial growth inhibition, as well as cytotoxicity for a human colon carcinoma cell line, was also dramatically enhanced by light. These data suggest that ravidomycin and desacetylravidomycin are potent photosensitizing, DNA-damaging agents.

Ionized calcium levels in coronary sinus blood during coronary angiography: effects of four contrast media.

The changes in ionized calcium level in the coronary sinus during coronary angiography were compared for four contrast media (meglumine sodium diatrizoate, iohexol, iopamidol, and meglumine sodium ioxaglate) in 44 subjects. Blood samples were collected before and 5, 15, and 30 seconds after injection of contrast medium into the left coronary artery. The hematocrit and ionized calcium level of each specimen were measured. Meglumine sodium diatrizoate produced the largest changes in hematocrit and ionized calcium level. The time-concentration curve of the hematocrit was similar for all four contrast media, but diatrizoate and ioxaglate produced a prolonged decrease of ionized calcium. The cause of this is not clear, but the phenomenon may be related to differences of ionic status among the contrast media. With respect to maintenance of the ionized calcium level, nonionic low-osmolality contrast medium with added calcium may be preferable for coronary angiography.

Acute electrolyte disturbances in coronary sinus during left coronary arteriography in man.

Electrolyte disturbances, particularly reduction of ionized calcium, induced by iodinated contrast media (CM) are important considerations in coronary arteriography. A study was conducted in 24 patients to evaluate the acute electrolyte alterations in the coronary sinus during left coronary arteriography. During left coronary arteriography, coronary sinus blood was withdrawn for measurement of electrolytes. The CM used were diatrizoate, ioxaglate, iohexol, and iopamidol. The hematocrit was decreased moderately by all 4 CM used at 5 s and returned to the control level at 15 s. The level of ionized calcium was decreased by all CM at 5 s. Prolonged reduction of ionic calcium was observed with diatrizoate and ioxaglate at 15 s. The level of potassium was almost unchanged by diatrizoate and ioxaglate in spite of hemodilution, which may lead us to a hypothesis that potassium can be released from the intracellular spaces such as red blood cells and vascular endothelial cells. Thus the depression of left ventricular function might be caused not only by reduction of ionized calcium, but also by a relative increase in the level of serum potassium.