To investigate the antigenic relationship between the macrophage and lymphocyte Fc receptors (FcR), a monoclonal antibody capable of blocking mouse macrophage Fc receptors was selected. Hybrids were formed by fusing the P3U1 mouse myeloma and spleen cells from a rat immunized with the mouse macrophage-like cell lines J774 and P388D1. The Fab fragment of the monoclonal IgG secreted by clone 2.4G2, inhibited the trypsin-resistant Fc receptor II (FcRII), which is specific for immune aggregates of mouse IgG1 and IgG2b, but had no inhibitory effect on the trypsin-sensitive Fc receptor I (FcRI), which binds monomeric IgG2a and erythrocytes coated with IgG2a. Thus, the monoclonal 2.4G2 IgG appeared to be specific for macrophage FcRII. Further evidence that the 2.4G2 IgG was directed against FcRII came from binding studies of the monoclonal antibody to J774 cells and a series of independently isolated variants which do not express FcRII. These variants of J774 bound 5% as much of the monoclonal antibody as the parent line, which bound 600,000 molecules of 2.4G2 IgG per cell. The antigenic relatedness of mouse lymphocyte FcR to mouse macrophage FcRII was demonstrated by the binding of 2.4G2 IgG to FcR-bearing lymphoid cell lines and the inhibition of the lymphocyte FcR by the monoclonal antibody. Preincubation of spleen cells and peritioneal cells with 2.3G2 IgG likewise inhibited rosette formation with ox erythrocytes coated with rabbit IgG. The ability of the hybridoma IgG to inhibit mouse FcRII was independent of the major histocompatibility complex. The 2.4G2 IgG antigenic determinant was not present on rat, guinea pig, rabbit, or human FcR-bearing cells.

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Characterization of a monoclonal antibody directed against mouse macrophage and lymphocyte Fc receptors.

Characterization of the continuous, differentiating myeloid cell line (HL-60) from a patient with acute promyelocytic leukemia

Publisher Summary This chapter discusses the intimate mechanisms of the regulation of antibody responses by T cells, the significance of these phenomena for the regulatory processes of the immune system, and their possible implication for the pathogenesis of various immunopathological states. The chapter adheres to popular terminology to refer to the two distinct classes of immunocompetent lymphocytes—T cells and B cells. The T cells are lymphocytes that have differentiated under the influence of the thymus and are responsible for mediating cellular immune reactions—such as delayed hypersensitivity and transplantation reactions. These cells participate in the development of humoral immunity but are not capable of secreting humoral antibodies. Because T cells stimulated by antigen respond by a clonal expansion and differentiation; and by being activated to perform their specific function, the former is elected as “educated T cells” and the latter as “activated T cells.” Activated T cells may result from stimulation by agents other than specific antigen. The B cells are lymphocytes that have differentiated under the influence of the bursa or its analog in mammals and ultimately become the effector cells in humoral immunity by the virtue of synthesizing and secreting immunoglobulin antibodies.

The regulatory influence of activated T cells on B cell responses to antigen.

Human peripheral lymphocytes were investigated for receptors binding Epstein-Barr virus (EBV) because of the regular association of this virus with infectious mononucleosis and Burkitt's lymphoma. This was done by a cytoadherence technique where virus-producing cells, displaying fresh viral determinants in their cytoplasmatic membrane, were mixed with lymphocytes. Unfractionated lymphocytes were found to adhere to these cells in contrast to column-purified T lymphocytes. The specificity of the binding was confirmed by blocking experiments that showed that sera containing high titers of antibodies directed against the virus could partially inhibit the adherence in contrast to low-titer sera. It is concluded that B lymphocytes, in contrast to T lymphocytes, have receptors for EBV. In a second line of experiments it was found that established human lymphoblastoid lines that carry the EBV genome had receptors characteristic for B lymphocytes and did not form T-lymphocyte rosettes. In contrast, a line of known T-lymphocyte origin that did not carry the EBV genome had receptors characteristic for T lymphocytes. EBV-transformed simian lymphoblastoid lines had surface markers indicating a B-lymphocyte origin in contrast to HVS-transformed simian lines that lacked surface immunoglobulin but carried receptors for sheep red blood cells.

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Surface markers on human B and T lymphocytes. II. Presence of Epstein-Barr virus receptors on B lymphocytes.

Publisher Summary This chapter discusses the biological activities of immunoglobulins of different classes and subclasses. This chapter illustrates that all immunoglobulins are composed of two types of polypeptide chains, heavy and light, which are linked by disulfide bonds. The biological activities of immunoglobulins may be divided into two categories: (1) the specific reaction with antigen and (2) the consequences of antigen - antibody reactions. The reaction with antigen has been called the primary function of immunoglobulins and is a property of the Fab fragment. This chapter reviews the biological activities that follow antigen-antibody reactions and that have been called the secondary functions of immunoglobulins. It has now been shown that the antibodies of the various classes and subclasses differ in their biological activities, and, in the future, one should attempt to determine how frequently restricted immune responses occur and how important such restricted antibody formation is in immune deficiency syndromes.

Biological activities of immunoglobulins of different classes and subclasses.

Evidence is presented for the existence on all B lymphocytes, but not on T lymphocytes, of a membrane-associated receptor for antibody. The receptor was detected by a radioautographic technique in which lymphoid cells were incubated with antibody followed by the corresponding radioiodinated antigen. The ease with which antibody eluted during washing indicated that the bond between antibody and cell was weak. The formation of an antibody-antigen complex on the cell surface, however, stabilized the bond and permitted accurate quantitation of cells with adherent antibody. The ability of several combinations of antibody and antigen to adhere to the cells demonstrated the nonspecificity of the phenomenon and emphasized the need for care in interpretation of antigen-binding studies particularly when immune cells are being used. The identity of antibody-binding lymphocytes was established by two different approaches. In the first, mouse lymphocyte populations greatly enriched for either T cells or B cells were examined. Their T cell content was assessed by means of well-established markers such as the θ C3H isoantigen. When this was compared with the number of antibody-binding cells, an inverse relationship was obtained in each instance; thus almost all thoracic duct cells from athymic mice labeled with an immune complex although none were θ positive. The striking reduction in antibody-binding cells observed in bursectomized chickens provided a second and independent line of evidence suggesting that B cells, not T cells, bind antibody. The ability of B cells from primed animals to bind antibody in vivo made it important to test whether this phenomenon was related to the carriage of immunological memory. No correlation was, however, found between membrane-bound antibody and memory. It was proposed that the existence of a receptor of this kind may provide a rational explanation for antibody-dependent killing of target cells and may prove of importance in antigen concentration particularly during the secondary response.

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J. Pye

Papers

A receptor for antibody on b lymphocytes : i. method of detection and functional significance

I. method of detection and functional signii~icance* $