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Five pregnant (two to three and one‐half months) Macaca fascicularisseroconverted following immunization with sucrose‐gradient purified and formalin‐inactivated whole simian immunodeficiency virus (SIVmac251). No untoward effects on fetal maturation were observed during the immunization of the mothers. Antibodies to SIVmac251(also those with in vitro neutralizing activity) were passively transferred to the offspring but disappeared within two to six months after birth. Antibodies to env glycoprotein (gp130) lasted longer than those against viral gag proteins (p26,p60).

In cynomolgus monkeys, we compared two human‐derived SIVmac251 whole virus vaccines, a long vs short immunization schedule, and two different challenge viruses. Both vaccines induced protection after challenge with human‐derived SIVmac251/32H. There was no difference between the two schedules of immunization. Seven monkeys, five of which were protected following the first challenge, were reboosted and rechallenged with monkey‐derived SIVmac251, but no protection was observed. The titers of anti‐human cell or ‐SIV neutralizing antibodies were not related to protection.

The kinetics of both erythroid burst-forming and colony-forming units (BFU-E, CFU-E) and myelomonocytic precursors [myelomacrophage colony-forming unit (CFU-C)] have been evaluated in tibial marrow, peripheral blood, and spleen of DBA/2 mice at time intervals after inoculation of either the anemic (FLV-A) or the polycythemic (FLV-P) strain of Friend leukemia virus. Either one of the viruses induced, at 7-10 days after infection, a massive increase in the number of BFU-Es in peripheral blood, in parallel with their depletion in tibial marrow and increase in spleen. A comparable increase in the blood BFU-E number was observed in splenectomized FLV-infected mice. These results indicate a marrow-spleen migration of BFU-Es. In spleen, the increase of the BFU-E number was associated with an increase in the CFU-E pool. In tibial marrow, a sequence of expansion/depletion waves occurred reciprocally at the level of BFU-E and CFU-E. The cycling of BFU-E([3H]thymidine in vitrosuicide index) in marrow, blood, and spleen was enhanced, whereas that of CFU-E and CFU-C showed little or no modification. These kinetic data suggest that the main target cell of FLV may be the BFU-E or a closely related element. In plates without added erythropoietin (but containing it in fetal calf serum), expression of CFU-E from FLV-P-treated animals was maximal; that of CFU-E from FLV-A-injected mice was either virtually absent or only slight in marrow or spleen, respectively. BFU-E growth always was fully dependent upon erythropoietin addition. Control studies in FLV-infected resistant mice and in susceptible mice given diluted or heat-inactivated virus provide convincing evidence that the phenomena described are induced by FLV.

The influence of in vivo infection with the polycythemic substrain of Friend leukemia virus on noninducible (‘natural’) resistance against allogeneic normal or malignant grafts was studied in lethally irradiated mice. Parallel studies were performed on the NK system in the same experimental conditions. The results indicate that FLV-P infection of mice with full (DBA/2) vs partial (BALB/c and CD2F1) susceptibility did not suppress their in vivo natural resistance against bone marrow or El-4 leukemia cells. On the other hand, a decline in NK activity paralleled the progression of leukemic disease in the more susceptible DBA/2 hosts.

To assess the prevalence of HIV-1 infection and study selected risk factors among patients attending a clinic for sexually transmitted diseases in Rome, 1442 outpatients seen consecutively between 20 February and 12 December 1989 were anonymously tested for anti-HIV-1. An evaluation of the trend of the HIV-1 infection was attempted by comparing the results of the present study with those obtained from a similar sample studied in 1986 in the same clinic. The overall estimated prevalence of anti-HIV-1 was 1.2 % among heterosexual non-drug user subjects and 16.1 % among homosexual or bisexual men. The anti-HIV-1 seropositivity was significantly higher in heterosexual subjects who reported sexual contact with intravenous drug users, as compared with those who did not report such exposure (12.5 % vs 0.8 %, p<0.005). Comparing the present data with those of a study conducted in 1986 in the same clinic, a lower prevalence of anti-HIV-1 was found among heterosexual subjects (1.2 % in 1989 vs 6.0 % in 1986, p<0.001). The availability after 1986 of several outpatient facilities attracting seropositive subjects and a change in the sexual behaviour of anti-HIV-1 positive subjects could explain this finding. Twenty percent of the heterosexual subjects and 62 % of the homosexual or bisexual men reported consistent use of condoms. In both heterosexual subjects and homosexual/bisexual men only the number of sexual partners in the previous year seemed to be related to the use of condoms, a higher proportion of subjects with two or more partners reporting the use of condoms, as compared with monogamous subjects (29.5 % vs 11.5 %, p<0.001 and 68.0 % vs 37.0 %, p<0.005). The infrequent use of condoms, in particular among heterosexual subjects, suggests that education campaigns conducted so far were partly effective.