Sensitization of cells and retroviruses to human serum by (αl-3) galactosyltransferase

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Abstract
MAMMALIAN C-type retroviruses are inactivated by human serum1,2, following triggering of the classical complement cascade3. This may have inhibited transmission to humans of C-type oncoviruses from other mammals1. Indeed, the retro-viruses human immunodeficiency virus and human T-cell leukaemia virus are resistant to human complement4,5. Antibody-independent activation of human Clq, the first component of the classical pathway, by retroviral envelope proteins has been described6. However, retroviruses produced from human cells are resistant to inactivation by human complement7,8 and human serum is known to contain antibodies directed against carbohydrates on retroviral envelopes9–11. Gal(αl–3)Gal terminal carbohydrates are expressed by most mammals but are absent in humans, which lack a functional (αl–3)galactosyltransferase gene12,13. Here, we demonstrate that anti-Gal(αl–3)Gal antibodies in human serum inactivate retroviruses produced from animal cells. Expression of porcine (αl–3)galactosyltransferase14–16 in human cells renders the cells and the retroviruses they produce sensitive to human serum.