Purification and N-terminal amino acid sequence comparisons of structural proteins from retrovirus-D/Washington and Mason-Pfizer monkey virus

A new D-type retrovirus originally designated SAIDS-D/Washington and here referred to as retrovirus-D/Washington (R-D/W) was recently isolated at the University of Washington Primate Center, Seattle, Wash., from a rhesus monkey with an acquired immunodeficiency syndrome and retroperitoneal fibromatosis. To better establish the relationship of this new D-type virus to the prototype D-type virus, Mason-Pfizer monkey virus (MPMV), we have purified and compared six structural proteins from each virus. The proteins purified from each D-type retrovirus include p4, p10, p12, p14, p27, and a phosphoprotein designated pp18 for MPMV and pp20 for R-D/W. Amino acid analysis and N-terminal amino acid sequence analysis show that the p4, p12, p14, and p27 proteins of R-D/W are distinct from the homologous proteins of MPMV but that these proteins from the two different viruses share a high degree of amino acid sequence homology. The p10 proteins from the two viruses have similar amino acid compositions, and both are blocked to N-terminal Edman degradation. The phosphoproteins from the two viruses each contain phosphoserine but are different from each other in amino acid composition, molecular weight, and N-terminal amino acid sequence. The data thus show that each of the R-D/W proteins examined is distinguishable from its MPMV homolog and that a major difference between these two D-type retroviruses is found in the viral phosphoproteins. The N-terminal amino acid sequences of D-type retroviral proteins were used to search for sequence homologies between D-type and other retroviral amino acid sequences. An unexpected amino acid sequence homology was found between R-D/W pp20 (a gag protein) and a 28-residue segment of the env precursor polyprotein of Rous sarcoma virus. The N-terminal amino acid sequences of the D-type major gag protein (p27) and the nucleic acid-binding protein (p14) show only limited amino acid sequence homology to functionally homologous proteins of C-type retroviruses.

Ia specific antilymphocyte antibodies in rheumatoid arthritis

Antilymphocyte antibodies (ALA) in rheumatoid arthritis (RA) have increased reactivity with phytohemagglutinin (PHA) activated lymphoblasts which are known to have increased expression of Ia antigen. The present experiments suggest that part of this reactivity represents an Ia specificity of ALA. Fifteen of 18 RA sera tested were able to inhibit the binding of monoclonal anti-Ia antibodies as measured by a rosette method. RA sera did not inhibit the binding of other monoclonal antibodies: anti-OKT3, anti-OKT4, and anti-OKT8. The ability of RA sera to inhibit the binding of anti-Ia antibody was eliminated after absorption of the RA sera with an Ia positive human cell line (B35M) but not by an Ia negative line (MOLT4). Blocking of anti-Ia binding was greater in the IgG fraction of the RA sera but also occurred in the IgM fraction. Experiments including ultracentrifugation, pepsin digestion of RA sera, and preincubation of lymphoblasts with aggregated IgG demonstrated that Fc binding by RA sera was not a factor. Both monoclonal anti-Ia and anti-Ia heteroantiserum also had increased reactivity with lymphoblast target cells. Pepsin digested Fab fragments of the anti-Ia heteroantiserum were able to block the activity of cytotoxic RA serum. However, ALA cytotoxic to lymphoblasts did not correlate with anti-Ia by rosette method. Ia-specific ALA by rosette method was associated with donor variability but did not appear to be HLA-DR restricted. Ia-specific ALA did correlate with disease activity. These data suggest that anti-Ia activity is present in RA sera and may play an immunoregulatory role in this disease.