Immune response to porins isolated from Salmonella typhi in different mouse strains.

Outer membrane proteins (OMPs) are able to induce protection against the challenge with S. typhi in a murine model. Both humoral and cellular immunity are involved in the protective mechanisms. In order to determine whether the responsiveness to S. typhi porins is genetically controlled in mice, different strains were immunized i.p. with 30 micrograms of OMPs isolated from S. typhi 9,12,Vi:d at days 0 and 7. On day 21, spleen cells were recovered and the lymphoproliferative response to porins was assessed. The highest responses were found in mice with H-2k and H-2a haplotypes (C3H/HeJ and A/J), intermediate responses were found in mice with H-2b haplotype (C57Bl/6) and the lowest responses in H-2d mice (Balb/c). These results demonstrate that the responsiveness to S. typhi porins is in part controlled by the major histocompatibility complex class II molecules and will help to further study the mechanisms of the immune response to these proteins.

Isolation and partial characterization of the amorphous cytoplasmic inclusions associated with infections caused by two potyviruses.

The potyviruses pepper mottle (PeMV) and watermelon mosaic virus-1, a strain of papaya ringspot (PRSV-W), induce the formation of a second type of cytoplasmic inclusion in addition to cylindrical (pinwheel) inclusions. The conspicuous aggregates of electron-dense material with imperfect spherical shapes have been called amorphous inclusions (AI). The AI were isolated from extracts of infected tissue using a combination of clarification with Triton X-100 and low-speed centrifugations through sucrose cushions. Electrophoresis, in sodium dodecyl sulfate-permeated polyacrylamide gels (SDS-PAGE), of the SDS-dissociated AI revealed a single constituent protein with a molecular weight of 51,000. SDS-PAGE-purified AI proteins were immunogenic and serologically unrelated to proteins of host, capsid, cylindrical inclusions, and tobacco etch virus nuclear inclusions. The AI protein of PeMV was distinct from the AI protein of PRSV-W on the basis of peptide analysis and serological tests. The antisera prepared to SDS-PAGE-purified AI proteins reacted specifically with Al in situ in immunofluorescence tests. The characteristics of the AI indicate that they are of viral origin.

Identification of potyviral amorphous inclusion protein as a nonstructural, virus-specific protein related to helper component.

Antisera to amorphous inclusion (AI) proteins associated with infections by pepper mottle virus (PeMV) and the watermelon mosaic virus-1 strain of papaya ringspot virus (PRSV-W) were used to probe in vitro translation products of the viral RNAs. The major translation product of PeMV RNA in the rabbit reticulocyte lysate (RRL) system was a previously reported polypeptide of apparent molecular weight 78,000 (Mr 78K). It reacted with anti-AI serum, whereas the major translation product in the wheat germ (WG) system was a 30K polypeptide that did not react with the antiserum. These results, the Mr values, and analyses of peptides generated by partial digestion with proteinase indicate that the amino acid sequences of the 30K polypeptide and the (Mr) 51K AI protein are distinct subsets of the 78K polypeptide amino acid sequence. Similar results were obtained with PRSV-W except that the Mr values of the corresponding translation products are 110K (RRL) and 60K (WG). Thus the 5'-most region of the PeMV and PRSV-W RNAs (corresponding to 78K and 110K, respectively) appears to encode two proteins rather than one as previously supposed on the basis of RRL translation products. Reciprocal serological tests revealed that the tobacco vein mottling virus aphid transmission helper component protein was related to AI protein. There is direct evidence that the AI represent another potyviral-coded nonstructural protein and the first evidence that a biologically functional protein is related to a component of a potyviral inclusion.