Daniel M. Takefman

Immune complexes containing human immunodeficiency virus type 1 primary isolates bind to lymphoid tissue B lymphocytes and are infectious for T lymphocytes.

ABSTRACT This study investigated the interaction of tonsil B lymphocytes with immune complexes containing human immunodeficiency virus (HIV IC) primary isolates and the infectivity of the B cell-bound HIV IC. Treatment of virus with a source of antibody and complement increased HIV IC binding to B cells by 5.6-fold. Most of the HIV IC that bound to B cells were not internalized but remained on the cell surface and were gradually released over 72 h. Cell-bound HIV IC were highly infectious for T cells while virus released by cultured B cells was only slightly infectious. Removal of HIV IC from the B-cell surface by protease treatment reduced the infection of T cells to near-background levels, indicating that infectious virus remained on the B-cell surface. These studies show that B lymphocytes can carry and transfer infectious HIV IC to T cells and thus suggest a novel mode of infection of T cells in lymphoid tissue that could be important for pathogenesis during HIV infection.

Detection and Characterization of Porcine Endogenous Retrovirus in Porcine Plasma and Porcine Factor VIII

ABSTRACT The pig genome contains porcine endogenous retroviruses (PERVs) capable of infecting human cells. Detection of infectious retrovirus in porcine peripheral blood mononuclear cells and endothelial cells suggested to us that pig plasma is likely to contain PERV. Both PERV env sequences and viral reverse transcriptase (RT) activity were detected in all plasma samples isolated from four NIH minipigs. To detect infectious virus from plasma, we performed a culture assay using three cell lines of feline, swine, and human origin that had previously been shown to be permissive for PERV. Infectious virus was successfully cultured from all four NIH minipig plasmas on the swine cell line ST-IOWA. Using RT-PCR with env-specific primers, we could detect expression of PERV class C envelope in the supernatant of ST-IOWA cells that had been exposed to each pig plasma. We next examined a pig plasma derivative, Hyate:C (porcine factor VIII), and found evidence of PERV particles, since all six lots examined were positive for PERV RNA and RT activity. However, infectious virus could not be detected in clinical lots of Hyate:C, suggesting that the manufacturing process might reduce the load of infectious virus to levels below detectable limits of the assay. Detection of infectious virus in porcine plasma confirms and extends the previous findings that certain porcine cells express PERV when manipulated in vitro and clearly demonstrates that there are porcine cells that express infectious PERV constitutively in vivo.

Human CD59 Incorporation into Porcine Endogenous Retrovirus Particles: Implications for the Use of Transgenic Pigs for Xenotransplantation

ABSTRACT Transgenic pigs have been engineered to express human CD59 (hCD59) in order to suppress hyperacute rejection of xenotransplants in human recipients. In this study, porcine endogenous retrovirus (PERV) was produced in a porcine cell line expressing hCD59 in order to examine the effect of this complement control protein on PERV neutralization by human sera. hCD59 was found to be incorporated into PERV particles produced from engineered ST-IOWA cells. PERV incorporation of hCD59 resulted in a dramatic inhibition of complement-mediated virolysis by human serum. However, incorporation of hCD59 had no effect on neutralization of PERV by human serum, as measured in infectivity assays. Our results suggest that the use of organs from hCD59 transgenic pigs will inhibit complement-mediated virolysis, but will not compromise the protective effects of human sera on the neutralization of PERV particles.

B lymphocytes in lymph nodes and peripheral blood are important for binding immune complexes containing HIV-1

We investigated the interaction of HIV immune complexes (HIV IC) with mononuclear cells from lymph nodes and blood. While antibody alone did not affect binding of HIV IC to mononuclear cells, antibody plus complement increased binding by as much as 10‐fold and complement alone also increased binding slightly. Most of the increased binding of HIV IC to mononuclear cells was blocked by heat‐inactivation of complement and by OKB7 monoclonal antibody, indicating that virus binding was to CR2 on B cells. A similar pattern of antibody and complement dependence for binding of HIV IC was observed with two model systems; Raji and Arent B‐cell lines. Most of the HIV IC that bound to lymph node cells were not internalized, but remained on the cell surface and were gradually released. However, even after 48 hr some HIV IC could be detected bound to cells. Under certain conditions, HIV IC were infectious for T cells if bound to B cells but not infectious if added directly to T cells. Additionally, HIV IC bound to B cells led to higher virus replication. These studies show that B lymphocytes from blood and lymph nodes can transfer infectious HIV IC to T cells.