Visna lentiviruses have a natural tropism for cells of the macrophage lineage of sheep and goats, but virus replication in these cells in vivo is restricted so that only small quantities of virus are produced. One restricting factor suggested in previous studies is that virus replication is dependent on the maturity of the cells: the more mature the cell, the less restrictive the replication of the virus. Since monocytes in peripheral blood are precursors of macrophages, we investigated the effect of cell maturation on virus replication under limited control conditions in vitro by inoculating blood leukocytes with virus and retarding the maturation of monocytes to macrophages during cultivation in serum-free medium. Using enzyme markers that identified the cells in their resting monocytic stage (peroxidase) and mature macrophage stage (acid phosphatase) along with quantitative in situ hybridization and immunocytochemistry with viral reagents to trace the efficiency of virus replication, we correlated virus replication with cell maturation. Only a few monocytes were susceptible to infection, and virus replication did not extend beyond a low level of transcription of viral RNA. In the acid phosphatase-positive, maturing macrophage, susceptibility of the cells to infection was increased and virus replication was greatly amplified to the level of translation of viral polypeptides. However, virus maturation was delayed by 3 days until further cell maturation had occurred. Thus, the entire life cycle of the virus, from its attachment to the target cell to its maturation in the cell, was dependent on the level of maturation/differentiation of the monocytic cell.

Lentiviruses, which cause arthritis-encephalitis and maedi-visna in goats and sheep, respectively, cause persistent infections in these animals. The viruses replicate productively at low levels in macrophages in diseased organs such as the "maedi lung" and nonproductively in other cell types such as leukocytes in peripheral blood. Nonproductive infections become productive during in vitro cultivation of the cells. This study showed that monocytes were the only cells in the peripheral blood leukocytes of an infected animal in which virus was detected and that virus activation occurred only when these cells matured into macrophages. Only a minute fraction of cultured monocytes matured into macrophages, and viral infectivity was associated exclusively with this fraction. Antiglobulincoated glass wool fragments were lethal for monocyte macrophages because of toxic phagocytosis, but had no effect on B or T lymphocytes. The simultaneous addition of the glass fragments and leukocytes to culture dishes resulted in no macrophage maturation and no virus production. The addition of the fragments to virus-producing macrophages caused the death of the cells and a decline in virus production. Virus production in less avidly phagocytic cells was unaffected by the glass. Thus, although macrophages may be permissive for virus replication, one mechanism for restricted virus expression in vivo may be physiological factors controlling the maturation of these cells.

To study the relationships between herpesviruses recently isolated from different pinniped species, antigenic and genetic analyses were performed. First, herpesviruses isolated from North American harbour seals (Phoca vitulina), a Californian sea lion (Zalophus californianus) and a European grey seal (Halichoerus grypus) were examined in an enzyme immunoassay (EIA) with a panel of monoclonal antibodies which had previously been shown to allow typing of herpesviruses from European harbour seals into two distinct virus types: phocid herpesvirus type-1 and type-2 (PhHV-1 and PhHV-2). The EIA data showed that all but one of the isolates from seals ranging in United States coastal waters were PhHV-2-1ike while the European grey seal herpesvirus was PhHV-l-like. Genetic characterization was facilitated by PCR analysis using primers based on conserved regions of the glycoprotein B and D (gB and gD) genes of the antigenically closely related canid (CHV) and felid (FHV) herpesviruses. Specific amplified products were obtained with five isolates antigenically characterized as PhHV-l-like but not with five PhHV-2-like isolates. Sequence analysis of the PCR products confirmed greatest similarity to members of the genus Varicellovirus of the Alphaherpesvirinae and in particular to CHV. Sequence analysis of two EcoRI fragments of the PhHV-2 genome (European isolate 7848) revealed greatest similarity to gammaherpesviruses and in particular equine herpesvirus-2. Although an unambiguous subgrouping was not feasible, this is the first evidence that PhHV-2 may be a putative gammaherpesvirus of pinnipeds.

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Understanding mechanisms responsible for meiotic resumption in mammalian oocytes is critical for the identification of strategies to enhance developmental competence of in vitro-matured oocytes. Improvement of in vitro oocyte maturation systems is dependent on a better understanding of mechanisms that regulate oocyte maturation both in vivo and in vitro as well as on the identification of methods to manipulate the meiotic progression of oocytes matured in vitro in a physiological manner. The purpose of this review is two-fold: first, to examine the mechanisms that underlie the acquisition of oocyte developmental competence and regulation of oocyte maturation in vivo and in vitro; second, to present data examining the role of transcription in mediating the ability of EGF and FSH to induce oocyte maturation in vitro. Results presented support the conclusions that (1) EGF-induced oocyte maturation does not require nascent gene transcription in both mice and domestic cats; (2) FSH requires gene transcription to induce oocyte maturation in both species; (3) EGF must be present in the maturation medium to optimize the effectiveness of FSH to promote oocyte maturation; (4) the mechanism used by FSH to induce oocyte maturation in vitro appears to predominate over that used by EGF when both EGF and FSH are present in maturation medium used for either murine or feline cumulus oocyte complexes.

Results suggest that FIV+ African lions develop lymphocyte deficiencies, including significant decreases in the absolute number of CD4+ and CD8+ T cells; these findings of immune dysfunction are similar to those defined for FIV+ domestic cats. It is important to monitor the number of CD4+ T cells in infected animals as a measure of disease progression.

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