The human cell-surface glycoproteins HuLy-m5, membrane co-factor protein (MCP) of the complement system, and trophoblast leucocyte-common (TLX) antigen, are CD46

D. F.J. Purcell, I. F.C. McKenzie, D. M. Lublin, P. M. Johnson, J. P. Atkinson, T. J. Oglesby, N. J. Deacon

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Abstract

The non-lineage restricted human CD46 antigen, with two glycoproteins of 56,000 molecular weight (MW) and 66,000 MW, was defined using a panel of monoclonal antibodies (mAb) that included the E4.3 mAb to the HuLy-m5 antigen. Here the E4.3 mAb is used to show that two other human cell-surface molecules, membrane co-factor protein (MCP) of the complement system and trophoblast leucocyte-common antigen (TLX), are the same as HuLy-m5; thus, these three independently identified molecules are equivalently CD46. A mouse mAb to TLX (H316) and a specific rabbit antiserum to purified MCP (RA-MCP) blocked the binding of FITC-labelled E4.3 to the surface of human peripheral blood leucocytes (PBL). In sequential immunoprecipitation studies, E4.3 cleared all molecules detected by H316 and the RA-MCP antiserum. Immunoprecipitation from Chinese hamster ovary cells expressing transfected MCP cDNA showed that E4.3 detects both the mature 66,000 higher MW form of MCP and its 48,000 MW pro-MCP precursor, which lacks O-linked carbohydrate and bears only simple high-mannose-type N-linked carbohydrate. The IgG fraction of a polyclonal antiserum to purified MCP blocked factor I-mediated cleavage of C3b, whereas the E4.3 mAb did not. These data establish that three independently identified antigen systems are indeed the same: HuLy-m5, which shares a cross-reactive epitope with some primate retroviral gp70 molecules and can be physically associated with class I major histocompatibility complex (MHC) chains in the cell membrane; MCP, of interest as a member of the regulators of complement activation gene family thought to protect autologous cells from complement activation; and TLX, a polymorphic molecule of interest for its potential role at the foeto-maternal tissue interface during pregnancy. Thus, the human CD46 antigen amalgamates the HuLy-m5, MCP and TLX cell-membrane glycoproteins.

Original languageEnglish
Pages (from-to)155-161
Number of pages7
JournalImmunology
Volume70
Issue number2
StatePublished - Jan 1 1990
Externally publishedYes

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    Purcell, D. F. J., McKenzie, I. F. C., Lublin, D. M., Johnson, P. M., Atkinson, J. P., Oglesby, T. J., & Deacon, N. J. (1990). The human cell-surface glycoproteins HuLy-m5, membrane co-factor protein (MCP) of the complement system, and trophoblast leucocyte-common (TLX) antigen, are CD46. Immunology, 70(2), 155-161.