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Fc-Receptors for IgG and IgM Immunoglobulins on Human T Lymphocytes: Mode of Re-Expression after Proteolysis or Interaction with Immune Complexes¹

From the Istituto di Microbiologia and Institute di Medicina del Lavoro, University of Genova, 16132, Genova, Italy, and Laboratory of Immunochemistry (I.N.S.E.R.M.U. 108) and the Research Institute on Blood Diseases, Hôpital Saint Louis, Paris

Abstract

The susceptibility to proteolysis and the mode of reexpression of receptors for IgM or IgG present on two different subpopulations of human T lymphocytes (T._M and T._G cells, respectively) have been investigated. The IgM receptor was highly susceptible to both trypsin and pronase, whereas the IgG receptor was resistant to trypsin and sensitive only to high concentrations of pronase.

The receptors have been removed by treating purified human T cells with pronase and their reappearance on the cell surface has been followed in vitro. The IgM receptors on the cell surface were detectable within 2 hr and the resynthesis was completed in 6 hr. IgG receptors were detectable in 4 to 6 hr and the resynthesis completed within 12 hr. When protein synthesis was inhibited by culturing the cells in the presence of cycloheximide for up to 12 hr, only the IgM receptor (which had a higher turnover rate) failed to be expressed. Whereas interaction of IgG immune complex with the IgG receptors was previously shown to induce a modulation of the receptors, contact with antigen-IgM antibody complexes did not alter the mode of expression of IgM receptors.

Footnotes

¹ This work was supported in part by Grant 76.7.0960 from D.G.R.S.T. and Grants CA 16673 and CA13148.