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Freeze/thaw (F/T) extracts of gradient purified concentrates of baboon endogenous retrovirus (BEV) depress phytohemagglutinin (PHA)-induced blastogenic transformation of human, baboon, and mouse lymphocytes. Extracts of normal fetal dog thymus cells (vehicle for virus replication), pelleted virus cores, spent tissue culture medium, and virus suspension buffers were not depressive. Sephacryl S-200 chromatography of BEV F/T extracts yielded two peaks of suppressive activity; peak A, eluted in the region of relatively high protein concentration with the 45,000-dalton ovalbumin marker, was highly labile, but not cytotoxic. Peak B, eluted between cytochrome cand DNP alanine markers, contained no detectable protein and appeared to consist of two components; one cytotoxic and highly labile and a second, noncytotoxic and relatively stable. A polyvalent antiserum to BEV proteins precipitated components of the BEV F/T extract and peaks A and B, but failed to abrogate immunodepression.

High-pressure oxygen (HPO) therapy for Pseudomonas aeruginosainfections of burn wounds has not been as effective as in vitro studies predicted. Mitigation of HPO toxicity for P. aeruginosaby nutrients present at the burn site could explain the lack of in vivo success. Alternatively, HPO-induced depression of host defense mechanisms could negate beneficial effects arising from HPOs known toxicity for P. aeruginosa.Accordingly, mouse peritoneal exudate cells (PEC), preincubated for 24 h in 1 atm of air-CO2, were used to study the in vitro effects of HPO or air-CO2on phagocytosis of P. aeruginosaor sheep erythrocytes (SRBC). Subsequent 2-h exposures of PEC to increasing numbers of bacteria, in an air-CO2atmosphere, decreased the percentage of bacteria cleared as well as PEC viability. Similar exposures of PEC to bacteria in an HPO atmosphere prevented the loss of PEC viability and increased bacterial clearance. In control experiments, increasing the number of SRBC relative to PEC decreased the percentage of SRBC cleared without decreasing PEC viability, as determined under air-CO2; short (2 h) exposure to HPO did not affect SRBC clearance. Microscopic examination of PEC indicated that a 24-h preincubation in HPO decreased the percentage of PEC which could ingest SRBC during subsequent experimental exposures (2 h) to air-CO2or HPO. These data suggest that short periods of exposure to HPO promote the ability of PEC to clear pseudomonads by adversely affecting the bacteria. This in turn prevents a pseudomonad-induced depression of PEC viability and function. In contrast, prolonged HPO exposure may be detrimental to phagocytic activity.

Virus isolates resistant to 1-[(2-hydroxyethoxy) methyl]-6-(phenylthio)thymine (HEPT) and a highly potent HEPT derivative, [1-benzyloxymethyl-5-ethyl-6-(α-pyridylthio)uracil] (NSC 648400, E-BPTU), were selected in cell culture. Cross-resistance evaluation indicated that the two drug resistant virus isolates were phenotypically distinct from one another although each of the virus isolates was resistant to both of the HEPT derivatives The virus isolate resistant to NSC 648400 had a single amino acid change in the reverse transcriptase (Y181C) which resulted in cross-resistance to all of the nonnucleoside reverse transcriptase inhibitors evaluated, with the exception of calanolide A. The NSC 648400-resistant virus isolate exhibited 15-fold enhanced sensitivity to calanolide A. The virus isolate selected in the presence of HEPT exhibited a single amino acid change (P236L) which was not cross- resistant to other nonnucleoside RT inhibitors tested with the exception of the two HEPT derivatives. This HEPT-resistant virus isolate exhibited enhanced sensitivity (5- to 10-fold) to thiazolobenzimidazole. We have used both virus isolates with defined single amino acid changes in the RT and bacterially expressed RTs with site-directed amino acid substitutions to test the effects of a wide variety of mutations on the activity of NSC 648400 Single mutations at amino acids 101, 103, 106, 181, or 236 yielded virus with high resistance (>20-fold) to NSC 648400, while lower levels of resistance were seen with mutations at amino acids 98, 100, or 108. These results suggest that several changes in the conformation of the nonnucleoside inhibitor binding site of the HIV-1 reverse transcriptase can affect the inhibitory activity of the HEPT class of compounds. Copyright 1995, 1999 Academic Press

Interferon induction and transient clearance of FV from the blood of leukemic mice are not sufficient by themselves to induce remissions. Of the interferon inducers tested, only statolon abrogates immunodepression, stimulates FV-cytotoxic antibody, and converts a rapidly lethal FV infection to a dormant state resulting in prolonged clinical remissions.We acknowledge the excellent technical assistance of Mrs. Jane Knight and Miss Eileen Rothman.

Statolon, an extract of the mold Penicillium stolonijerumcontaining a double stranded RNA mycophage, can convert a rapidly lethal Friend leukemia viral (FV) infection into a dormant one (1-5). One inoculation of statolon, administered when FV is disseminated throughout the body, induces interferon and FV-cytotoxic antibody thereby suppressing both virus and virus-transformed cells (2, 5). This suppression results in a long lasting clinical remission during which no infective Friend virions can be detected (1, 4). The FV genome is present however, as shown by the spontaneous emergence of FV leukemia late in the life of mice with dormant infections and by the leukemogenicity of spleen cells transferred from mice with dormant infections to normal mice (3).Interferon production leads to suppression of FV replication, but by itself cannot completely suppress the disease; poly I:C and Newcastle disease virus can produce as much interferon as statolon, clear the blood of FV but cannot convert FV leukemia into a dormant infection (2).Production of humoral antibody against both virus and virus transformed cells appears to be crucial for development of the FV-dormant state. Untreated FV leukemic mice have no demonstrable antibody and are considered immunosuppressed in this regard, although high titers of circulating virus may mask the presence of antibody. Numerous investigators have used the immune response to sheep erythrocytes (SRBC) to evaluate the immunocompetence of FV-infected mice (6, 10). These workers have demonstrated repeatedly that the response to this antigen in infected mice is severely depressed relative to normal levels.In this report we describe preliminary investigations of immunological reactivity to SRBC in FV-infected and statolon-treated mice. Using the Jerne and Nordin assay for hemolytic antibody plaque forming cells (anti-SRBC PFC) (11), we found that statolon abrogates the FV-induced immunodepression of the anti-SRBC response.