Activation of lymphocytes alters Fc receptor-beta 2-microglobulin interrelationship on the lymphocyte surface

An Fc receptor structurally related to MHC class I antigens

Maternal immunoglobulin G transmitted to the fetus or newborn provides humoral immunity for the first weeks of mammalian life. Fc receptors on intestinal epithelial cells of the neonatal rat (FcRn) mediate the uptake of IgG from milk. Affinity-purified FcRn is resolved by SDS-PAGE into components of relative molecular masses 45,000-53,000 (p51) and about 14,000 (p14). We report the identification of the smaller component as beta 2-microglobulin. Association of beta 2-microglobulin with p51 was confirmed by crosslinking in intestinal epithelial cell brush borders. We have cloned a cDNA encoding the presumptive Fc-binding subunit, p51, and its predicted primary structure has three extracellular domains and a transmembrane region which are all homologous to the corresponding domains of class I major histocompatibility complex (MHC) antigens. This is the first time a function has been assigned to an MHC antigen-related molecule.

The different effect of alpha and gamma interferons and interleukin 2 on the expression of CD2, CD3, CD4 and CD8 antigens in comparison to histocompatibility antigens of human lymphocytes

The effects of alpha- and gamma-interferons (IFN-alpha, -gamma) and of interleukin 2 (IL-2) on the expression of certain differentiation antigens were compared with those of major histocompatibility antigens on human lymphocytes. IFN-gamma and IFN-alpha in high doses significantly increased the expression of T11 (CD2) differentiation antigen, but did not affect the expression of T4 (CD4), T8 (CD8), T3 (CD3) and Leu-7 antigens (HNK-1). Both natural and recombinant IFN-alpha and -beta apparently increased the expression of HLA-ABC antigens and of beta-2 microglobulin (beta 2m) after 16 h incubation. The amount of HLA-DR antigen, however, doubled in a few hours following IFN-gamma treatment. IL-2 affected the expression of CD2 and CD8 antigens only marginally, but did not affect that of CD3 and Leu-7; however, it strongly enhanced the expression of HLA-ABC, HLA-DR, and beta 2m antigens.

Regulatory function of cell surface molecules CD2-, LFA- and beta 2-microglobulin in natural killer cell activity

The functional importance of various cell membrane bound molecules was studied and compared in the NK cytotoxicity and CTL activity. LFA-1 and CD2 participate in both killing functions, while CD3 and CD8/CD4 as well as MHC class I molecules are involved only in CTL activity. Nevertheless CD2- and beta 2-microglobulin are representatives of the NK function. It was demonstrated that CD2-, LFA-1 and beta 2-microglobulin molecules have an additive and complementary function in the killing mechanism. The upregulation of alpha- and gamma-interferons on NK function seems not to be a consequence of the enhanced expression of these molecules on the cell surface induced by IF at the same time.

C3 cleaved by membrane proteases binds to C3b acceptors expressed on concanavalin A-stimulated human lymphocytes and enhances antibody-dependent cellular cytotoxicity

On activation of cells membrane-associated proteases--including serine esterases known to cleave the third component of complement (C3)--become expressed. In this paper it is shown that as a consequence of this enzyme activity isolated native human C3 added to concanavalin A (Con A)-activated human lymphocytes is cleaved on the surface of the blast cells. This enables the immediate fixation of nascent C3b (C3bx) through its short-lived metastable binding site to C3b acceptors (C3bA's) newly expressed on Con A-stimulated cells. Acceptor-bound C3b is detected by the immune adherence rosette formation of the C3-treated Con A blasts with the C3b receptor (C3bR)-bearing O, Rh+ erythrocytes (32 +/- 4%). The cleavage of C3 and the covalent fixation of C3b are shown to be inhibited by phenylmethylsulphonyl fluoride and methylamine, respectively. As a functional consequence of the covalent fixation of C3b to the mitogen-activated lymphocytes it is demonstrated that the antibody-dependent cellular cytotoxicity (ADCC) of these cells against O, Rh+ erythrocytes sensitized with anti-D IgG is significantly enhanced. The C3 specificity of the process and the role of C3bR's of the target cells are proved. It is postulated that effector cell-bound C3b amplifies ADCC by improving effector cell-target cell contact.