Autoantigenic properties of native and denatured glutamic acid decarboxylase: evidence for a conformational epitope.

The frequency of antibodies to GAD (anti-GAD) in insulin-dependent diabetes mellitus (IDDM) varies greatly according to the type of assay employed. We therefore examined the immunoassay characteristics of diabetic sera using GAD purified from porcine brain and shown to contain both isoforms. Sera from 38 patients with IDDM, including 1 patient with both stiff-man syndrome (SMS) and IDDM, were studied for anti-GAD by radioimmunoprecipitation (RIP), Western blotting, and dot-blotting. The sera were selected according to reactivity in the RIP assay. There was a good correlation between potency of the RIP reaction at the screening dilution of 1:2 and the endpoint dilution in the assay which ranged from 1:2 to 1:30,000 for IDDM sera, and 1:300,000 for the SMS serum. Of the 38 sera positive for anti-GAD by RIP, only 6 had antibodies detectable by Western blotting, and all gave an RIP titer of at least 1:250. The low frequency of antibodies by Western blotting was explicable by denaturation of the antigen. Thus, using a dot-blotting assay in which reactivity to untreated "native" GAD was compared with reactivity to GAD after denaturation by reduction with 2-mercaptoethanol and boiling, 20 of the 38 IDDM sera reacted unequivocally with the native GAD compared with only 2 that reacted with denatured GAD after reduction and boiling. The sera were tested for their capacity to inhibit the catalytic activity of GAD, but only the high-titer serum from the patient with SMS did so. Our study further validates the RIP assay for anti-GAD and establishes that anti-GAD exists in IDDM over a wide range of titers that correlate with other assay characteristics, and also indicates that the conformational autoantibody epitope on GAD is susceptible to alteration under denaturing conditions.

Cutaneous protothecosis presenting as recurrent chromomycosis.

Chromomycosis and protothecosis are both rare cutaneous infections. We report a case in which protothecosis mimicked a relapse of chromomycosis both clinically and on special stains. The chromomycosis responded to local excision and ketoconazole therapy. The protothecosis failed to respond to ketoconazole but resolved with combined amphotericin B and tetracycline hydrochloride therapy.

Effect of rifampin and bacitracin on nasal carriers of Staphylococcus aureus.

Anterior nares cultures from 664 hospital personnel identified 165 (24.8%) as carriers of Staphylococcus aureus. Persistent carriers (17.8%) were identified and randomly assigned to one of four treatment groups: rifampin (600 mg once a day for 5 days), bacitracin ointment (topically applied three times a day for 10 days), combined rifampin and bacitracin, and control (no treatment). Bacitracin ointment was ineffective in eliminating S. aureus from the anterior nares and had a postreatment carrier rate equal to the control rate. Rifampin therapy caused a highly significant reduction (79%) in carriage; however, combined therapy was not as effective as treatment with rifampin alone. Of 132 strains of staphylococci isolated before and after treatment, all were susceptible to less than 0.016 micrograms of rifampin per ml. This study demonstrates that rifampin may be an effective antistaphylococcal antibiotic and could be used to control the carrier state in high-risk situations.

Parotitis: clinical presentations and management.

Although mumps virus is the most common and, therefore, best known cause of parotitis, other causes are not infrequent and need to be distinguished from mumps. Knowledge of the various clinical presentations of parotitis and judicious use of a few ancillary tests will facilitate differential diagnosis.