AEGiS-11IAC: The dynamic expression of CD4 on cultured monocytes: implications for in vitro HIV infection.

11th International AIDS Conference

Vancouver, British Columbia — July 7-12, 1996

The dynamic expression of CD4 on cultured monocytes: implications for in vitro HIV infection.

Int Conf AIDS 1996 Jul 7-12; 11:56 (abstract no. Mo.A.1001)
Graziani GM, Filion LG; University of Ottawa, Department of Microbiology/Immunology, Faculty of Medicine, Ottawa, ON, CA. Fax: 613-562-5452. E-mail: g507794@labsunl.med.uottawa.ca.

INTRODUCTION: Following overnight culture of purified monocytes, or monocytes in a PBMC (peripheral blood mononuclear cell) fraction, CD4 is down-regulated. However, within the PBMC cultures, CD4 on T cells continues to be expressed, suggesting that CD4 regulation is cell-specific. Whereas much work has been done on T cell CD4 regulation and the role of p56lck and serine residues within the cytoplasmic tail, little is known about the regulation of CD4 on monocytes.

OBJECTIVES: To determine the fate of monocyte CD4 following overnight culture, and to determine the mechanisms responsible for the down-regulation. We hypothesized that monocyte CD4 is internalized following overnight culturing, and that this internalization is triggered by the adherence of the monocytes to the culture surface as they undergo differentiation into culture-derived macrophages. Furthermore, we proposed that the differential regulation of CD4 on monocytes and T cells may be the result of differential signal transduction pathways, specifically at the level of the serine residues, which would be reflected by differences in the transmembrane and/or cytoplasmic tail sequences of the molecule. Methods &

RESULTS: Flow cytometric analysis revealed that the down-regulation of monocyte CD4 is the result of internalization of the molecule (n = 10). Culturing PBMCs in Teflon vials (which inhibit adherence) and in gelatin/fibronectin coated flasks suggests that the down-regulation of monocyte CD4 is not mediated by adherence (n = 3). RT-PCR and automated sequencing of the CD4 molecule of uncultured, purified peripheral blood monocytes and a promonocyte cell line (U937s) reveals that their transmembrane and cytoplasmic domains are identical to that of the published T cell sequence.

CONCLUSIONS: We conclude that monocyte CD4 is internalized following overnight culturing. However, adherence of the monocytes to the culture surface does not appear to mediate this internalization. Furthermore, the transmembrane and cytoplasmic sequences of monocyte and T cell CD4 are identical, suggesting that the differential expression of the molecule by each cell type is not a consequence of differences at the level of the serine residues. These results may have important implications with respect to the in vitro role of CD4 as the major receptor for HIV in monocytes and macrophages.

Keywords: AEGIS, Antigens, CD4, Monocytes, HIV Infections, Macrophages, HIV, HIV Envelope Protein gp120, Down-Regulation, T-Lymphocytes, HIV Seronegativity, In Vitro, Animal, genetics, immunology, ICA11

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