Membrane immunoglobulins and antigen receptors on B and T lymphocytes

Sequences related to immunoglobulin kappa chain messenger RNA in T cells

We investigated by molecular hybridization whether T cells contain RNA sequences homologous to RNA which codes for immunoglobulin kappa-chain (k-chain). A radioactive probe of complementary DNA (cDNA) was prepared by transcription of purified k-chain mRNA from mouse myeloma MOPC-41 with reverse transcriptase (RNA-dependent-DNA nucleotidyltransferase) from avian myeloblastosis virus. The cDNA probably corresponded only to the constant region and 3'-terminus of k-chain mRNA. Kappa-chain cDNA was found to hybridize efficiently with RNA from both thymus cells and an established culture of thymoma cells. The thymus and thymoma cells contained 99.8% and 100% theta-positive cells, respectively. Quantitatively the average thymus T cell (thymus derived lymphocyte) contained about one half as much k-chain mRNA as the average spleen B cell ("bursa" dependent lymphocyte), whereas the thymoma cells contained only 1/33 as much. Control hybridizations of k-chain cDNA with myeloma and liver RNA support the conclusion that T cells in the thymus and in the thymoma cell line synthesize k-chain mRNA-like molecules. The thermal stability of hybrids of k-chain cDNA with RNA from spleen, thymus, thymoma, and another k-chain producing myeloma tumor was lower than that with MOPC-41 RNA. This finding may be due to the existence of several slightly different ck genes in the mouse as suggested by various control experiments.

Long-term immunoglobulin G production by transplanted thymus cells

Two sublines of CBA/H mice congenic for the Igl allotype locus were used to study donor-allotype IgG2a concentrations in the serum of mice injected intravenously with thymus cells. High concentrations (up to several mg/ml) were found in x-irradiated recipients (exposed to 650 rad, or to 900 rad with a restorative injection of fetal liver cells). The highest concentrations were seen 1-2 months after injection, but detectable quantities were still present in most individuals after 377 days. No donor-allotype Ig was detected in non-irradiated recipients. Cell for cell, lymph node cells were about as efficient as thymus cells at transferring IgG production. Although pluripotent hematopoietic stem cells were found in the thymus, their concentration (about 10(-8)) was too low to account for the results. It is suggested that the thymus contains B lymphocytes, or their precursors, with considerably greater powers of self-maintenance and expansion than are possessed, on average, by the B lymphocytes in lymph nodes.

Frequency of precursor cells against the enzyme beta-galactosidase: an estimate of the BALB/c strain antibody repertoire

A method has been developed for detecting anti-beta-galactosidase antibodies after isoelectric focusing in thin layers of polyacrylamide gel. By "staining" with wild-type enzyme, all antibodies against beta-galactosidase are detected, while a subset of antibodies able to activate a mutant enzyme is detected by staining with that enzyme. Limiting dilutions of beta-galactosidase-primed or unprimed spleen cells of BALB/c mice were transferred together with antigen into sublethally irradiated syngeneic hosts. The limiting role of the precursor B cells has been judged by the analysis of the clonal distribution of galactosidase-specific antibodies in recipient sera. The frequency of anti-wild-type beta-galactosidase precursor cells was one in 0.42 x 10(6) in the primed and one in 0.93 x 10(6) in the unprimed spleen. The frequency of precursor cells for antibodies activating the mutant enzyme was one in 1.5 x 10(6) in the primed and one in 4.6 x 10(6) in the unprimed spleen. Therefore four and five times less anti-M (mutant) than anti-B (wild-type) precursor cells exist in the spleens of primed and unprimed BALB/c mice, respectively. Comparing 51 clones derived from one primed donor mouse, it was possible to demonstrate that at least 43 different mutant-beta-galactosidase-activating antibodies can be produced in one mouse. Comparing these 43 clones with 27 clones derived from another donor mouse, only one clone seemed to be common to both mice. From this the repertoire of the BALB/c strain has been estimated to consist of over 1000 different mutant enzyme-activating antibodies.

Biosynthesis of membrane bound Ig and secretion of Ig by chicken lymphoid cells

The metabolic turnover of membrane proteins of chicken lymphoid cells is studied, using a double isotope labeling technique (i.e., [14C]amino acid pulse and [3H]leucine chase). Compared with other membrane proteins, the metabolic turnover of membrane bound immunoglobulins (M-Ig) is very slow. There was no difference in the turnover between M-Ig and specific antigen binding receptor immunoglobulins. Immunoglobulins appear to be a stable constituent of the lumphocyte membrane. Cellular kinetic experiments show that the rate of biosynthesis of secreted immunoglobulins (S-Ig) is nearly ten times as much as that of M-Ig, suggesting that metabolic pathway leading to M-Ig are distinct from those leading to S-Ig. The difference in 3H/14C ratios between S-Ig and M-Ig reflects the rate of biosynthesis of these immunoglobulins by two types of bursa derived lymphoid cells.

The lymphocyte plasma membrane: locus of control in the immune response

The lymphocyte plasma membrane is the locus of events which control the immune response. T and B lymphocytes, which mediate cellular and humoral immunity respectively, show distinctive plasma membrane morphologies and cell surface receptors. The dynamic state of these plasma components is emphasized by their lateral mobility in the fluid plane of the membrane, as well as variation in their structure or expression as the lymphocyte proliferates and differentiates in response to stimulation by antigen or mitogens. The best understood membrane glycoproteins are surface membrane immunoglobulins that serve as antigen receptors on B cells, and the histocompatability-beta2 microglobulin complex that has an immunoglobulin-like structure. Other less well defined surface structures showing modulation during the cell cycle may affect growth regulation of proliferating lymphocytes. Some of these are shared by fetal and neoplastic cells. Major theories of lymphocyte signaling are discussed, and the early events in lymphocyte activation are reviewed. While a complete model encompassing all these early events is not yet possible, the central issues can be usefully discussed in term of receptor-transducer-effector concepts derived by strong parallels from a knowledge of hormone-membrane interactions.

Evolutionary and developmental aspects of T-cell recognition

Studies relating to the nature of the antigen-specific T-cell receptor are reviewed in the light of present knowledge of phylogenetic and ontogenetic development. It is suggested that this evidence supports the concept that immunoglobulin (Ig) is the T-cell receptor, and that the following conclusions may be tentatively drawn.

Immunoglobulin-bearing and complement-receptor lymphocytes constitute the same population in human peripheral blood

Complement-receptor lymphocytes have generally been considered to be a subpopulation of bone-marrow derived (B) lymphocytes. However, the present studies show that essentially all cells with integral surface immunoglobulin from normal human peripheral blood bear receptors for the third component of complement. Moreover, after removal of phagocytes, all cells with complement receptors bear surface Ig. Thus, circulating B cells and complement-receptor lymphocytes are the same population.

Calcium-sensitive modulation of Ig capping: evidence supporting a cytoplasmic control of ligand-receptor complexes

Capping of anti-Ig-Ig complexes was studied in murine B lymphocytes. Morphological studies indicated that caps formed rapidly on cells before any changes in shape. The first changes in cell shape were evident as a contraction right under the cap area. The removal of extracellular calcium had no effect on cap formation. Furthermore, the introduction of calcium by the ionophore A-23187 stopped capping. The ionophere by itself in the absence of extracellular calcium had no effect. Caps were found to be disrupted, the complexes scattering over the entire cell surface if the cells were treated by A-23187 after the caps had formed. The disruptive effect of A-23187 as dependent on extracellular calcium and could be stopped by drugs that affected energy metabolism. The cytochalasins also disrupted the formed caps. Drugs that affect energy metabolism by themselves did not disrupt the caps. We interpret the effects of the ionophore as resulting from a systemic hypercontractility of microfilaments. A theory for explaining the formation and disruption of capping is discussed.

Membrane Ig on MPC11 myeloma cells: correlation between the expression of membrane Ig, a receptor for Ig and the process of secretion

The expression of membrane immunoglobulin (mIg) was examined in three cloned MPC11-derived mouse myeloma cell lines. Membrane immunofluorescence studies demonstrated that IgG2b producer cells (P1) had complete IgG molecules, L-chain producer (L1) had only L-chain determinants and nonproducer (NP2) did not have any Ig determinants on the cell surface. An Ig receptor, with characteristics different from B lymphocyte Fc receptor, has been found to be present on secreting cells (P1 or L1), but not on the NP2 cell variant. The data reported in the present paper indicate that the expression of mIg and of the Ig receptor molecule is clearly correlated with the process of secretion. In the light of previous data reported on Ig secretion, a model is proposed which correlates the process of secretion with the expression not only of mIg, but also of the receptor for Ig.

B and T cell lymphomas. Analysis of blood and lymph nodes in 87 patients

B and T cell populations were studied in blood and neoplastic tissues from 64 untreated and 23 treated patients with non-Hodgkin's lymphoma. This study was undertaken primarily to evaluate the relation of B and T cell markers in various lymphomas to the currently accepted morphologic classifications and to determine the utility of various tissues in defining the cell of origin of a lymphoma. When histologically involved blood, bone marrow, lymph nodes or body fluids were studied, a B or T cell origin of the lymphoma was identified in 26 of 28 (68 per cent) patients. A B cell origin was found in 17 adults classified as having nodular (N) or diffuse (D) poorly differentiated lymphocytic lymphoma (PDLL). One lymphoma of T cell origin was observed in an adult with poorly differentiated lymphocytic lymphoma-diffuse (PDLL-D). In contrast, all cases of PDLL-D in children were T cell in origin. The origin of American Burkitt's (stem cell) lymphoma in two children was the B cell. When histologically involved blood was studied, a B or T cell origin was demonstrated in 10 of 21 (48 percent) adults. Evidence of a monoclonal proliferation of B lymphocytes in the blood was found two adults with more than 7 per cent lymphoma cells in Wright-Giemsa stained blood smears. When neoplastic lymph nodes were studied, the diagnosis of a B cell lymphoma was made in 8 of 12 (67 per cent) adults. Study of surface markers on malignant cells in cerebrospinal or serosal fluids frequently revealed a B or T cell origin of the lymphoma. B and T lymphocyte numbers in the blood did not correlate with immunoglobulin or skin test abnormalities. Abnormalities in circulating B or T cell percentages at diagnosis were a poor prognostic sign in patients with PDLL-D.

Lymphocyte surface immunoglobulins

Immunoglobulins have been isolated from the surface of B (bone marrow-derived) and T (thymus-derived) lymphocytes. Two types of membrane immunoglobulin occur on B lymphocytes; one type resembles the 200,000-dalton subunit of IgM, the second possesses a heavy chain electrophoretically distinct from mu chain and does not correspond to any of the known classes of mouse immunoglobulins. It might correspond to human sigma chain. T lymphocytes possess only one type of surface immunoglobulin. This molecule has a mass of approximately 200,000 daltons and contains light chains and heavy chains similar to, but not identical to, mu chains. Evidence now exists that surface IgM-like immunoglobulins of B lymphocytes and T lymphocytes activated to certain antigens can bind specifically to antigen. These observations suggest that surface immunoglobulin functions as a receptor for antigen on B cells and at least on some T cells. The mechanisms by which combination of antigen with surface immunoglobulin initiate differentiation remain to be determined.

Separation and functional analysis of subpopulations of lymphocytes bearing complement and Fc receptors

A highly versatile procedure is described in this review which can be used to separate and obtain in pure form subpopulations of lymphoid cells which express different cell surface structures. The method is based on the observation that when rosetting and non-rosetting leukocytes are centrifuged on a cushion of Isopaque/Ficoll, the rosetting leukocytes and red cells sink whereas the non-rosetting leukocytes float. Thus, any subpopulation of leukocytes can be separated providing they can be identified by rosetting. The earlier sections of this review describe the method, its efficiency of separation and its advantages compared with other fractionation procedures. Subsequent sections describe experiments in which the procedure was specifically applied to separating Fc receptor (Fc+) and complement receptor (CR+) lymphocytes. On the basis of these two receptors it was possible to subdivide T and B lymphocytes into distinct subpopulations. Four subclasses of B lymphocytes were identified in mouse spleen (Fc+CR+,Fc+CR-,Fc-CR+ and Fc-CR-) and two subclasses of T cells were also detected (Fc+ and Fc-). The functional relevance of these subpopulations of lymphocytes was examined. It was found that in all cases examined, antigens could successfully activate CR+ B cells to produce antibody. However, only polymeric antigens, whether T-dependent or T-independent, were capable of triggering CR- B cells to synthesize antibody. Furthermore, preliminary experiments suggest that Fc receptors are present on functional B cells and helper T cells but are not expressed on cytotoxic T cells. On the basis of these results it is proposed that complement receptors on B lymphocytes provide an additional binding site which stabilizes the union between the antigen-specific receptors and soluble antigen. In contrast, due to their multi-determinant nature, polymeric antigens can avidly bind to B cells without involvement of the complement receptors. The possibility of Fc receptors playing a similar role in stabilizing the interaction of antigen with specific receptors on lymphocytes, particularly on T helper cells, is also discussed.

Biochemical and enzymatic characterization of thymic and splenic lymphocyte plasma membranes from inbred rats

Purified splenic and thymic lymphocytes from the ACI and F344 strains of inbred rats were disrupted by controlled hypotonic treatment, and their plasma membranes were prepared by sucrose density gradient centrifugation. The plasma membrane preparations were highly purified as judged by the structural appearance of the smooth membrane vesicles, by the 10- to 15-fold enrichment of 5'-nucleotidase, which cytochemically localized exclusively in the plasma membranes of intact lymphocytes, by the high cholesterol to phospholipid molar ratio (0.7-1.0), and by the very low specific activities of the enzymes associated predominantly with mitochondria, lysosomes, and endoplasmic reticulum. The protein and the lipid contents of the membranes were 48-55 and 37-48%, respectively. The total lipid content of plasma membranes was characteristically higher in thymic than splenic lymphocytes from both ACI and F344 strains. The specific activity of 5'-nucleotidase was similar in splenic lymphocyte membranes of the ACI strain, and in both the thymic and splenic lymphocyte membranes of the F344 strain. In contrast, the thymic lymphocyte membranes in the ACI strain showed half as much 5'-nucleotidase specific activity. Cytochemical results indicated that the 5'-nucleotidase is located on the outside surface of the lymphocyte plasma membranes.

How infection can trigger autoimmunity

The role of infection in the development of autoimmunity is discussed in view of recent advances in the field of immunologic tolerance. Infectious agents may directly damage immune function by impairing the mechanisms of discrimination between self and non-self antigens; alternatively they may "deceive" the immune system by presentation of self-determinants in an immunogenic form or by uncovering of normally sequestered antigenic determinants. The first of these two pathogenetic mechanisms may be responsible for generalized and the second for selective autoimmune reactions. Different clinical conditions are evaluated on the basis of these concepts. The interaction of personal factors with infection and autoimmunity is also taken into consideration.

Lymphocyte plasma membranes. III. Composition of lymphocyte plasma membranes from normal and immunized rats

Isolated plasma membranes of thymic and splenic lymphocytes from unimmunized and immunized rats of the inbred ACI and F344 strains were analyzed for chemical and enzymatic composition, for membrane protein patterns by polyacrylamide gel electrophoresis and for membrane-associated immunoglobulins. After immunization, the thymic and splenic lymphocyte membranes from F344 rat contained less carbohydrate and higher phospholipid contents than control animals. In both ACI and F344 inbred rat strains the membrane phospholipid to cholesterol weight ratio increased significantly after immunization. The electrophoretic patterns of solubilized membrane proteins and of iodinated external membrane proteins were similar in unimmunized and immunized animals. When thymic and splenic lymphocytes of normal or immunized animals were surface radioidinated, solubilized in Triton X-100, NP-40 or 10 M urea in 1.5 M acetic acid and analyzed by immunoprecipitation, labeled IgM immunoglobulin was recovered from thymic lymphocytes but both labeled IgG and IgM were recovered from splenic lymphocytes. However, when unlabeled isolated plasma membranes were solubilized in 1 percent Triton X-100 and analyzed by immunodiffusion in agarose gels both IgG and IgM were identified in thymic and splenic cells.

Membrane immunoglobulins of B lymphocytes: inability to detect certain characteristic IgM and IgD antigens

Hemagglutination and fluorescent antibody studies have provided strong evidence for the unavailability or absence of specific antigenic sites on membrane-bound IgM which are present in serum and intracellular IgM. Antisera specific for different parts of the molecule indicated that a portion but not all of the Fc was involved. Absorption experiments with normal and leukemic viable B lymphocytes failed to remove a population of Fc antibodies found in IgM-specific antisera. Similar findings were made for IgD, the other major membrane immunoglobulin of human peripheral blood B cells. Various interpretations of these observations are discussed. The most likely possibility appears that the C-terminal portion of the heavy chains of the immunoglobulin molecule is buried in the membrane.