Immunomodulatory effect of synthetic peptides corresponding to sequences within the CH2 and CH3 domain of human IgG1

Functional studies on Fc receptors

Fc receptors (FcRs) are cell surface molecules that recognize and bind to the constant domains of immunoglobulins. In doing so, they enable antibodies to perform several biological functions, by forming a link between specific antigen recognition and FcR-bearing cells. Here, Gabriella Sármay provides an overview of recent studies on FcRs in Hungarian laboratories, concentrating on their role in selected biological systems.

Synthetic peptides comprising defined sequences of CH-2 and CH-3 domains of human IgG1 induce prostaglandin E2 production from human peripheral blood mononuclear cells

Synthetic peptides Y48 and Y75 comprising sequences at exposed sites within the CH-2 and CH-3 domains of human IgG1 at a concentration of 10(-5) M, increase PGE2 production by human peripheral blood mononuclear cell (PBMC) cultures. An increase of leukocyte migration inhibitory factor (LMIF) production in PBMC cultures--as a result of synthetic peptide treatment--was also observed. This LMIF activity, to some extent, is attributed to the PGE2 production by the cells; the inhibition of leukocyte migration being abolished by the presence of indomethacine or antibody to PGE2.

Effect of human IgG1 peptides on the antigen-specific antibody response of mice in vivo

The effect of synthetic peptides--corresponding to the amino acid sequences 289-301 (Y48) and 293-301 (Y91) within the CH-2 domain in the human IgG1 was studied on the oxazolone-specific primary and secondary antibody response isotype distribution and on the sheep erythrocyte (SRBC)-specific primary IgM response. High responder (Balb/c) and low responder (C57Bl/6) mice to oxazolone hapten were treated intraperitoneally with various doses of peptides simultaneously with the first and second contact sensitization. The relative levels of oxazolone-specific IgM, IgG3, IgG1, IgG2a and IgG2b antibodies were determined by a solid phase radioimmunoassay. Y48 and Y91 peptides in a dose range of 10(-5) - 10(-8) M/animal enhanced the oxazolone-specific antibody response. This effect was more striking under suboptimal conditions: using smaller antigen dose for sensitization, cyclophosphamide pretreatment or using genetically low responder mice. SRBC-specific primary IgM response was enhanced by Y91 peptide, Y48 was ineffective.

Modulatory effect of synthetic human IgG Fc peptides on the in vitro immune response of murine spleen cells

Synthetic peptides representative of defined surface-exposed sequences within the CH-2 and CH-3 domains of human IgG1 induce IgM production by murine spleen cells, even in cultures depleted of T-lymphocytes. This stimulation was not altered by simultaneous administration of dextran sulphate in suboptimal concentration, its effect being additive to that of the peptides. Cell proliferation was augmented only at 10(-4) M doses of peptides. IL-1 production by adherent cells was also increased as a result of peptide treatment; whilst administration of exogenous IL-1, 4 h later, seemed to abrogate the effect of peptide treatment on the augmentation of IgM production. Peptide treatment failed to induce IL-2 and/or IL-4 production. The effect of IgG peptides seems to be exerted directly on B-cells at an early step of activation and to be mediated at least in part by IL-1.

Rheumatoid factor and Fc signaling: a tale of two Cinderellas

Signaling to lymphocytes depends not only upon the interaction of receptors with specific antigen, but also upon antigen nonspecific receptors which receive input from two classes of molecules, immunologically specific end products and lymphokines. These represent the central elements in the physiologic stimulation of immune responses to both self and foreign antigens. This review is dedicated primarily to describing the function of physiologically active receptors for end product which are central to end product feedback in normal immune responses. The emergence of autoimmunity as a pathologic process resultant from a defective end product signaling mechanism is described.