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A distinguishing feature of the mixed connective tissue disease (MCTD) syndrome is the presence in the serum of antibody in high titer to ribonucleoprotein (RNP). To determine whether this was an exclusive observation, a large rheumatic disease population was surveyed for the presence of antibody in high titer to extractable nuclear antigens (ENA) including RNP. Of 650 sera examined, 440 (from 240 patients) had antinuclear antibody. Only 39 patients had serum antibody to ENA in titers greater than or equal to 1:200 dilution. In 16 the anti-ENA was shown by RNAse digestion to be anti-RNP. Although many clinical and laboratory characteristics were similar in these two groups, the patients more closely resembled the previously described MCTD syndrome and, importantly, less often had severe renal and central nervous system disease manifestations. Thus the presence of serum antibodies to ENA that are predominantly RNAse-sensitive (anti-RNP) helps to identify a rheumatic disease syndrome and also appears to have prognostic value.

By use of a microlymphocytotoxic assay to detect 32 HLA antigens of the A and B series, we examined 49 Mexican-American adults with acute rheumatic fever and contrasted the findings with 100 ethnically identical controls. Eighty-nine percent of the total possible antigens were identified. Strong associations between HLA antigens from either locus and acute rheumatic fever were not detected. These findings serve to emphasize the importance of nongenetic factors in the pathogenesis of acute rheumatic fever and help clarify the role of HLA antigens in rheumatic diseases.