Use of fluorescent antibodies in the study of lymphoid cell membrane molecules

Sequence analysis of rat integrin alpha E1 and alpha E2 subunits: tissue expression reveals phenotypic similarities between intraepithelial lymphocytes and dendritic cells in lymph

The integrin alpha OX-62 subunit is defined by the OX-62 monoclonal antibody that was raised against rat dendritic cells in lymph (veiled cells) and shows properties similar to those of human alpha E2 that is predominantly expressed on intraepithelial lymphocytes. To clone alpha OX-62, rat probes generated using primers specific for the human alpha E sequence were used to screen rat T cell cDNA libraries. cDNA clones encoding two similar but not identical alpha subunits that are closely related to but distinct from human alpha E were isolated. alpha E1 is predicted to be the rat homolog of mouse alpha M290 and alpha E2 corresponds to rat alpha OX-62. Immunofluorescence analysis revealed that mouse alpha E1 and rat alpha E2 are expressed in dendritic epidermal T cells in the skin, intraepithelial lymphocytes in the small intestine and in cells with a dendritic morphology present at sites where gamma delta T cells occur in lymphoid organs. Unexpectedly, alpha E2 is co-expressed with intracellular CD3-delta and a 33-kDa CD3 chain but not the T cell receptor in veiled cells. These findings suggest that veiled cells may be derived from a lymphoid precursor. Furthermore, veiled cells show phenotypic similarities to intraepithelial lymphocytes.

Monoclonal antibody 1D8 detects an activation-related molecule on human B lymphocytes and on a minor T-lymphocyte subpopulation

A novel murine monoclonal antibody (MAb) 1D8 was produced after immunization with the nylon wool-adherent fraction of human peripheral blood mononuclear cells (PBMNC). Its reactivity pattern was studied on a panel of hemopoetic normal cells, cell lines and malignancies. Mab 1D8 detects a lymphocyte-specific surface antigen expressed on a major subpopulation of mature B lymphocytes as well as on a minor T-cell subset. Activation-related changes in the expression of 1D8 molecule were observed on both B and T lymphocytes. As compared with the pattern of known activation-associated antigens, 1D8 seems to play a role in the early stages of lymphocyte activation. The antigen could not be immunoprecipitated by the conventional methods for glycoproteins.

Suppression of B cell differentiation by ligation of membrane-bound IgM

Using B cells from the transgenic mouse line B6-Sp6 and control littermates, stimulated by lipopolysaccharide (LPS) under novel culture conditions that provide for the response of all B cells, we show here that specific ligation of the surface IgM molecules always results in inhibition of terminal differentiation and immunoglobulin secretion by activated cells, regardless of the ligand. Thus, monoclonal antibodies to (a) the CH region of Ig (anti-mu and anti-allotype), (b) the C kappa region, (c) the V region (anti-idiotype) of surface IgM, as well as (d) multivalent antigen (2,4,6-trinitrophenyl-bovine serum albumin), all show similar effects and dose-response curves. IgD-negative transgenic B cells are equally sensitive to IgM ligation-dependent inhibition, as control (IgD-positive) B cells. The allotype specificity of this inhibition, assessed by using anti-mu allotype reagents to inhibit and assay the responses, suggests that B cells expressing transgenic or endogenous IgM in transgenic B6-Sp6 mice are largely independent populations. These observations establish that anti-IgM antibodies in conjunction with appropriate LPS stimulation, provide a universal model system for functional characterization of B cell responses.

Normal serum immunoglobulins influence the numbers of bone marrow pre-B and B cells

The homeostatic mechanisms controlling B lymphocyte output from bone marrow are not well understood. The present experiments evaluated putative influences of circulating immunoglobulins (Ig) on bone marrow (BM) pre-B and B cell populations. Injections into normal mice of Ig isolated from normal mouse serum, resulted in a dose-dependent and reversible reduction in numbers of BM B lineage cells, in particular of small B220+ surface IgM- cells. Maximal effects were observed upon injection of isologous polyclonal Ig and were independent of mature T cells. These results suggest a feedback modulation of peripheral Ig on cellular activities in BM B lineage compartments, mediated by mechanisms that seem to involve the variable regions of the Ig molecule.

Stimulation of B and T cells by in vivo high dose immunoglobulin administration in normal mice

Adult BALB/c mice were injected intravenously with a preparation of pooled normal murine IgG (400 mg/kg/day, on five consecutive days) and studied 8, 15, and 60 days later. High dose IgG administration increased the total numbers of splenic activated B and CD4+ (but not CD8+) T cells, as well as the numbers of splenic Ig-secreting cells, particularly in the IgG isotypes. Reactivities to some autoantigens, but not to bacterial or other heteroantigens, were selectively amplified amongst IgM-secreting cells. IgG administration did not alter the specific primary immune response to heterologous erythrocytes or bacterial dextran. No cellular alterations were detected in the lymph nodes or peritoneal cavity of treated animals. Most of these effects subsided with time, but some autoantibody reactivities remained elevated 60 days later. The present results suggest that the therapeutic effects of high dose IgG administration which have been reported in human diseases might be associated with the immunostimulatory activities of such treatment.

Structure of the T cell antigen receptor (TCR): two CD3 epsilon subunits in a functional TCR/CD3 complex

Transgenic mice carrying and expressing the human CD3 epsilon gene incorporate the corresponding protein product into T cell receptor (TCR)/CD3 complexes on thymocyte and T cell surfaces. The chimeric antigen receptors allow normal T cell development and selection of repertoires in vivo and are able to transduce activation signals in vitro. We have exploited the ability to distinguish mouse (m) and human (h)CD3 epsilon chains to analyze the stoichiometry of CD3 epsilon in transgenic mouse TCRs. Immunoprecipitation and fluorescence resonance energy transfer experiments demonstrate that such TCRs can contain both h- and mCD3 epsilon chains, implying that more than one CD3 epsilon subunit occurs per TCR. Antigen comodulation studies are consistent with a stochastic use of h- or mCD3 epsilon during receptor assembly, and further suggest a structure for the TCR/CD3 complex with two CD3 epsilon chains. The determination of CD3 epsilon subunit stoichiometry, together with existing biochemical data, allows the generation of a minimal model for the structure of the TCR and illustrates the potential value of the transgenic approach to the analysis of complex receptors.

Selective peripheral expansion and activation of B cells expressing endogenous immunoglobulin in mu-transgenic mice

Two different lines of C57BL/6 mice (IgHb) carrying complete rearranged mu chain genes from BALB/c (IgMa) were analyzed for the expression and secretion of endogenous as well as transgenic immunoglobulins at the level of single cells. Quantitation of B cells expressing endogenous IgMb by cytofluorometry, limiting dilution analyses of clonal precursors and secretory cell assays revealed a marked selective expansion, activation and terminal differentiation of those cells producing endogenous immunoglobulins. Thus, the very infrequent IgMb-bearing B cells produced in bone marrow of transgenic mice accumulate in spleen, where they are activated and account for roughly half of all natural immunoglobulin-secreting cells. These observations indicate that mu-transgenic mice are valuable in studies of the antibody repertoire selection operating in unprimed animals but their use could be misleading in the analyzing "monoclonal" immune system.

Extensive splenic B cell activation in IgM-transgenic mice

Two lines of IgM-transgenic mice were analyzed for the state of activation of their splenic compartment, with regard to the frequency of large cells in the different lymphoid subpopulations, and to the isotype distribution of background plasma cells. We observed an extensive B cell activation preferentially involving B lymphocytes co-expressing transgenic and endogenous IgM (IgD), and resulting in massive immunoglobulin class switch. Nearly all splenic plasma cells contain endogenous immunoglobulins, with frequencies of IgG and IgA plasma cells significantly higher than in normal mice. There are virtually no plasma cells that produce only the transgenic IgM. Moreover, only a proportion of plasma cells producing endogenous immunoglobulins co-express the transgenic product. In addition to these observations that apply to both transgenic lines, differences were found between the two lines concerning the quantitative expression of the transgenic IgM, the frequency of cells expressing the transgene and the magnitude of switch. These data are indicative of the complexity of the IgM-transgenic mouse model, in which the phenomenology may depend on the transgene insertional position, on B cell physiology and on immunological mechanisms of recognition, induction and regulation.

Different large deletions of T cell receptor V beta genes in natural populations of mice

A panel of geographically separate Mus m. domesticus and Swiss mice from several sources was screened for deletions in the T cell receptor variable (V) beta locus. Four out of forty-three strains tested show a deletion identical to or larger than the deletion previously described in SJL mice. To our knowledge, this is the first time that such important V beta deletions are described in inbred or partially inbred wild-derived strains of mice. On the other hand there seems to be very little polymorphism between the remaining V beta genes. Expression of V beta genes in peripheral and intra-thymic T cells was tested using antibodies specific for different V beta polypeptide chains. Flow cytometry analysis revealed a high expression of V beta 6 and V beta 17 genes in the Copacabana Swiss-derived strain and an absence of V beta 17 expression in the WLA wild-derived strain. The three Mus m. domesticus strains (WLA, DDO and WBG) having deleted two to three additional V beta subfamilies compared to SJL present no apparent immune deficiencies or autoimmune disorders. We conclude that relatively few V beta genes may suffice for unimpaired survival of wild mice and that there is a selective pressure for the structural conservation of the remaining V beta genes.

Periodic organization of the contractile apparatus in smooth muscle revealed by the motion of dense bodies in single cells

To study the organization of the contractile apparatus in smooth muscle and its behavior during shortening, the movement of dense bodies in contracting saponin skinned, isolated cells was analyzed from digital images collected at fixed time intervals. These cells were optically lucent so that punctate structures, identified immunocytochemically as dense bodies, were visible in them with the phase contrast microscope. Methods were adapted and developed to track the bodies and to study their relative motion. Analysis of their tracks or trajectories indicated that the bodies did not move passively as cells shortened and that nearby bodies often had similar patterns of motion. Analysis of the relative motion of the bodies indicated that some bodies were structurally linked to one another or constrained so that the distance between them remained relatively constant during contraction. Such bodies tended to fall into laterally oriented, semirigid groups found at approximately 6-microns intervals along the cell axis. Other dense bodies moved rapidly toward one another axially during contraction. Such bodies were often members of separate semirigid groups. This suggests that the semirigid groups of dense bodies in smooth muscle cells may provide a framework for the attachment of the contractile structures to the cytoskeleton and the cell surface and indicates that smooth muscle may be more well-ordered than previously thought. The methods described here for the analysis of the motion of intracellular structures should be directly applicable to the study of motion in other cell types.

Transplantation tolerance correlates with high levels of T- and B-lymphocyte activity

Mice tolerized (treated to make them tolerant) at birth to transplantation antigens by injection of semiallogeneic cells contain very high numbers of activated T and B lymphocytes in their spleen. Lymphoid hyperactivity correlates with the tolerant state: it is present only in animals accepting skin allografts. Tolerized mice that reject the allogeneic skin graft have approximately the same numbers of total and activated lymphocytes as normal mice. The high level of lymphocyte activation in tolerant mice persists for up to 1 year of age, although it declines with age, and is markedly increased by a secondary allograft. The magnitudes of both primary and secondary tolerant responses are significantly higher than the immunological response of a normal mouse rejecting the same type of allograft. These observations contradict concepts of clonal deletion or anergy as the basis of neonatally induced transplantation tolerance and may contribute additional approaches to experimentation and control of transplantation reactions.

Natural lymphocyte activation in postnatal development of germ-free and conventional mice

The degree of activation of B and T cells in the developing spleen during postnatal life was studied in germ-free (GF) and specific-pathogen-free (SPF) BALB/c mice of the same breeding stock. We found that the progeny of GF mothers up to 3 weeks of age contain higher numbers of activated splenic cells than baby SPF mice, thus suggesting qualitative differences in maternally-derived antibodies. This "advantage" of GF mice is also indicated by an anticipated maturation of the splenic lymphoid compartment and is reflected in higher frequencies of B and T lymphocytes in adult life. In both kinds of mice, the frequency of activated cells is very high at birth and then declines, reaching minimal values by 4 weeks of age. Later, activated B cells increase sharply in SPF mice, suggesting polyclonal activation mediated by bacterial products. Results are discussed on the basis of the mutual influences between B and T cells in the establishment of a functional network.

Strain differences in the postnatal development of the mouse splenic lymphoid system

Four strains of mice, CBA/J, BALB/c, C57BL/6J and B10.BR, were studied for cellular composition of the developing spleen in postnatal life. Considerable strain differences were found in the absolute numbers of splenic lymphoid cells at various ages, the frequencies of B and T cells, the L3T4/Lyt-2 ratio and the time of appearance of IgD and class II antigen on B cells. These observations are discussed in view of strain differences described for the acquisition of immune responsiveness and for susceptibility to tolerance induction in neonates. Finally, it was found that the expression of I-E antigen is delayed compared to that of I-A in ontogeny and possibly during B-cell differentiation as well.