The origin of cell surface immunoglobulin of marrow-derived and thymus-derived lymphocytes of the rat

Immigration of thoracic duct B lymphocytes into established germinal centers in the rat

Immigration of B lymphocytes into established germinal centers in the rat was studied by transferring genetically marked thoracic duct B cells to non-irradiated congenic hosts at various times between 3 days before and 6 days after host immunization. Seven days after host immunization, the distribution of donor B cells to lymph node germinal centers (relative to their distribution to non-germinal center lymph node areas) was measured by two-color flow cytometry in which (a) donor and host B cells were distinguished by their Ig kappa chain allotypes, and (b) germinal center B cells were distinguished by their lack of labeling with the monoclonal antibody HIS22. Thoracic duct B cells from long-term antigen-primed rats were found to immigrate into host germinal centers much better than B cells from unprimed donors. This effect was antigen specific: primed B cells only immigrated well into host germinal centers induced by the priming antigen. Although B cells localized in germinal centers most efficiently when injected before immunization, specifically primed donor B cells injected after immunization were still found to be at least as evenly distributed to germinal centers as to other lymph node areas, whereas unprimed B cells transferred after immunization localized poorly in host germinal centers. These findings are discussed in light of recent suggestions that memory B cell clones are maintained by continued antigenic stimulation within secondary lymphoid follicles.

The host component of the popliteal lymph node graft-versus-host reaction. Selective representation of lymphocyte subsets and the requirement for alloantigenic incompatibility between donor cells and activated host B cells

We have examined the cellular changes taking place in rat popliteal lymph nodes undergoing a graft-versus-host (GvH) reaction. Examination of immunoperoxidase-stained lymph node sections, using a panel of mouse monoclonal antibodies directed against different rat lymphoid cell subsets, revealed a disorganization of the lymph node architecture with disappearance of the follicles, and an intermingling of T and B cells, so that no distinct T- and B-cell areas were visible any more. Since the GvH nodes showed a preferential accumulation of host B cells over host T cells (particularly over the W 3/25+ T helper cell subset), we also investigated the requirements for host B cell activation. The popliteal lymph node GvH reaction was induced in (PVG X DA)F1 rats by the injection of PVG cells into one foot and by DA cells into the other foot, and then immunoglobulin kappa allotype marked PVG B cells from athymic donors were injected intravenously. The allotype marked B cells proliferated vigorously in response to the DA T cells, but much less in response to the PVG T cells. These results indicate that the massive B-cell activation taking place in GvH reactions may require an alloantigen incompatibility between donor T cells and host B cells, and argue against non-specific mitogenic induction of the B cells.

Antibody-dependent cellular cytotoxicity (K) and natural killing (NK) in B-suppressed germ-free nude rats

The influence of the thymus and the possible requirement for surface immunoglobulin expression for the development of K and NK activity were assessed in rats. This species was chosen in preference to mice as they show good levels of K-cell activity. Studies were carried out in athymic (rnu/rnu) rats some of which were treated from birth with rabbit anti-rat IgM antibody to suppress B-cell development. The results indicate that normal levels of both K and NK activity develop in the spleens of 6-8-week-old athymic rats, which do not contain cells expressing surface membrane immunoglobulin. While K and NK cells show characteristics of the lymphoid lineage, neither the thymus nor surface membrane immunoglobulin expression appears to be required for development of normal levels of these cytolytic activities.

The still elusive T cell receptor: on the possibility of a common V-gene pool for B- and T-cell-antigen receptor molecules

The contention that VH constitutes a part of T-cell receptors for antigens was probed by purifying rabbit T cells and analysing these cells for non-immunoglobulin VH, i.e. VH not associated with L chain. A number of anti-VH antisera were employed for this purpose, the most important being goat antiserum, reacting with common a1 allotype determinants (allotype determinants expressed on free VH and H chain as well as on intact immunoglobulins), rat antibody against common non-allotype VH determinants (VH framework determinants expressed on VH and H chain as well as on intact immunoglobulins) and chicken antibody against unmasked non-allotype determinants (VH determinants accessible only in the absence of L chain). VH and L chain was quantified by radioimmunoassays on extracts and supernatants from unstimulated T cells as well as from T cells stimulated by concanavalin A and by allogeneic cells. Absolute depletion of Ig-containing and -producing cells was not achieved but in no case was an excess of VH over L chain observed. This indicated that all detected VH originated from cells of the B lineage. The cells were also cultured in the presence of labelled amino acids followed by analysis of detergent extracts and supernatants by immunoadsorption and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) fluorography. Again, no evidence for T-cell VH could be found. Affinity purified anit-VH antibody was used to label viable rabbit T cells through the use of secondary fluorescence-labelled anti-immunoglobulin antibody. No VH-specific labelling of T cells could be observed. Mixed lymphocyte cultures were carried out in the presence of affinity-purified anti-VH antibodies. No inhibition of the reaction could be discerned. The failure to detect T-cell VH is in agreement with the recent finding that the VH-genome in T cells is not rearranged in a functional manner similar to that in B cells.

A repopulation assay for B and T lymphocyte stem cells employing radiation chimaeras

The repopulation of the peripheral lymphoid compartment of lethally-irradiated rats reconstituted with lymphopoietic stem cells was studied. Cell lineages were traced by using genetic markers of cell surface molecules: immunoglobulin allotype for B lymphocytes and peripheral T cell alloantigen for T lymphocytes. Provided the markers had been bred on to a genetic background congenic with the hosts, they conferred neither an advantage nor disadvantage in competition with unmarked cells. The degree of chimaerism measured the lymphopoietic activity of the restorative inoculum. The most potent activity was found in foetal liver and spleen; next was infant spleen and bone marrow; then young adult bone marrow. Peripheral lymphoid tissues showed very little activity and thymus cells were inert. This tissue distribution, the stability of the chimaerism and the substantial expansion of numbers from the injected cells all point to the assay measuring an early stem cell. The overlap of subpopulations of lymphocytes in the rat thoracic duct was studied. A method for the conjugation of fluorescein to antibodies while they are attached to immuno-adsorbent affinity columns is also described.

Periodontal bone loss and immune response to ovalbumin in germfree rats fed antigen-free diet with ovalbumin

A technique for the characterization of rat gingival lymphocytes has been described. The technique was used to obtain gingival cells from rats maintained on antigen-free diets or such diets with ovalbumin (OVA) added. Increases in gingival lymphocyte numbers in the antigen-fed (AF) animals occurred by 16 to 23 days of OVA feeding. The elevated gingival lymphocyte numbers were predominantly T lymphocytes at the initial intervals of the experiment (to 59 days of OVA feeding). At 128 days of OVA feeding T-lymphocyte numbers diminished but B-lymphocyte numbers increased, and AF animals had more than six times as many gingival B lymphocytes as animals not fed antigen. Also, AF animals showed immunoglobulin A antibody in intestinal perfusates (after 9 days of OVA feeding) and in saliva (within 23 days of OVA initiation). Plasma immunoglobulin G antibodies were not detected until 59 days of feeding. Spleen cells from AF rats showed in vitro blastogenic responses to OVA at 23 to 59 days of feeding. Periodontal bone loss was greater in AF animals after 59 and 128 days of OVA. Germfree animals fed only one antigen experienced more periodontal bone loss than animals fed the same diet not containing antigen. Therefore, immune phenomena can contribute to experimental bone loss in germfree rats.

Receptors for IgM on human lymphocytes. I. Detection of receptors on freshly drawn lymphocytes and at physiological temperature

Receptors for the Fc portion of IgM (RFcmu) have previously been found to be primarily associated with the T lymphocyte subpopulation in humans, and their detection has frequently required overnight incubation of the cells before assay. In the present study, using highly sensitized indicator cells (EAmu), lymphocytes with receptor for IgM (EAmu-RFC) were detected immediately after isolation from human peripheral blood. Identification of EAmu-RFC on freshly isolated lymphocytes was greatly facilitated by assay at room temperature (RT) or 37 degrees C, implying that analogous interactions between IgM-antigen complexes and lymphocytes with receptor for IgM normally occur in vivo. These results seem to indicate that some RFcmu on lymphocytes may be occupied by IgM and/or IgM-antigen complexes in vivo and that immediately after isolation many RFcmu are still occupied and unavailable for interaction with EAmu. It is suggested that the successful competition of IgM-antigen complexes for RFcmu on T lymphocytes is the signal for and/or mechanism of expression of help by the lymphocyte. The sensitivity of the assay for EAmu-RFC also permitted the identification of a small subpopulation of RFcmu+ lymphocytes in the non-T cell fraction of the peripheral blood of some individuals.

Recognition of antigens by T lymphocytes

The present review briefly summarizes our knowledge of antigen-specific B and T lymphocyte receptors. Antigen-specific receptors on mammalian B lymphocytes are mainly monomeric IgM and IgD consisting of conventional immunoglobulin heavy and light chains. The nature of the T lymphocyte receptor which can specifically recognize antigens is not yet fully defined. However, it seems that conventional light chains do not participate in the build up of this receptor, and that the receptor is made up of heavy chains of a new immunoglobulin class which has to be further characterized and which we call Tau-chain. The variable region of the T lymphocyte receptors share idiotypic determinants with the corresponding B lymphocyte receptors. The possible linkage between the T cell idiotypes present on the Tau-chains and molecules which are under the control of genes of the Major Histocompatibility Complex of the species are discussed. In the last part of the review two methods for the induction of specific transplantation tolerance in adult animals are described. These methods are based on the concept that T lymphocytes reactive against alloantigens bear idiotypic determinants against which a specific auto-immune response can be initiated.

T-lymphocyte heterogeneity in the rat: separation of functional subpopulations using a monoclonal antibody

W3/25 antibody is the monoclonal product of a hybrid cell resulting from the fusion of a mouse myeloma cell line with spleen cells from a mouse immunized with rat thymocytes. Pure clones have been derived, and segregants free of parental myeloma chains have been isolated. Previous studies have shown that this antibody recognizes a subpopulation of T cells among rat thoracic duct lymphocytes. In the work reported here, three T-cell functions were assayed after separating rat thoracic duct lymphocytes on the fluorescence-activated cell sorter on the basis of labeling with W3/25 antibody. Two of the functional activities appeared to be completely segregated by this procedure. Thus, helper cell activity for an anti-hapten plaque-forming cell response was confined to the labeled population, whereas the allogeneic suppressive effect produced in a parental vector F1 adoptive transfer was mediated by cells in the unlabeled fraction. The third function, graft-versus-host activity, was almost entirely contained within the labeled subpopulation. It is concluded that the antigenic determinant recognized by the monoclonal antibody W3/25 is a differentiation marker for T-cell functional subpopulations.

Reassortment of lymphocytes in lymph from normal and allografted sheep

The distribution and nature of surface immunoglobulin-bearing (SIg) cells were studied in various sources of lymph from normal sheep and from sheep bearing renal autografts and renal allografts. In normal sheep, 12.2% +/- 1.5 of all mononuclear cells in peripheral lymph SIg and, of these, more than 50% were monocytes and macrophages. Less than 6% of the lymphocytes in peripheral lymph carried SIg. In contrast, 24.7% +/- 1.3 of the mononuclear cells in central lymph had SIg, and all of the labeled cells were lymphocytes. The frequencies of SIg cells in peripheral lymph issuing from renal autografts and from renal allografts were 6.7% +/- 1.3 and 6.9% +/- 0.8, respectively, and the labeled cells were predominantly lymphocytes. The proportion of SIg cells in central lymph from graft-bearing sheep was similar to that from normal sheep. The differences between central lymph and peripheral lymph from both normal and graft-bearing sheep are thought to reflect a restriction on the passage of SIg cells through capillary endothelium in nonlymphoid tissues.

Estimation by radioimmunoassay of VH determinants (Aa1) associated with rabbit T lymphocytes

A radioimmunoassay with specificity for the a1 allotype determinant of rabbit immunoglobulin (Ig) heavy chains was used for the quantitation of VH in detergent extracts of lymph node cells from a1a1/b4b4 rabbits. B cell-derived Ig in the same extracts was estimated with a radioimmunoassay specific for L-chain. About 2 X 10(5) molecules/cell was found by both assays when assuming a molecular weight of 1.5 X 10(5) dalton. Extracts prepared from lymphocytes depleted of B cells (surface Ig+ cells) were also found to contain corresponding amounts of a1 and L-chain, with values varying from about 10(3) to 10(4) molecules/cellmthe estimates were not influenced by the presence of inhibitors of proteolytic enzymes. Supernatants, obtained after keeping the lymphocytes in culture for 16 h, were analyzed by the same methods. Again, matching amounts of a1 and L-chain were found in supernatants from nonfractionated as well as from B cell-depleted populations. The results obtained indicate that T cells do not carry or produce an excess of a1 compared to L-chain, as would have been expected if the T cell antigen receptor carried the same variable region as the Ig heavy chain while being otherwise composed of nonimmunoglobulin-like structures.

Lymphocyte surface immunoglobulins: detection, characterization, and occurrence in disease of the lymphoid system

Surface immunoglobulins (Igs) of lymphocytes are of considerable interest because these molecules probably function as receptors for antigen, and knowledge of their molecular properties should provide information on the mechanisms of immune differentiation. The density and types of surface Ig on a cell provide markers useful in indicating the class of a lymphocyte and its stage of maturity. Moreover, knowledge of the specificities of the surface Ig of neoplastic lymphocytes might suggest the nature of agents involved in the generation of the disease. Two broad classes of lymphocytes, bone marrow-derived lymphocytes (B cells) active in antibody secretion, and thymus-derived lymphocytes (T cells) which mediate cellular immune reactions, and their subpopulations must be considered with reference to the nature, origin, and function of their surface immunoglobulin. This article analyzes direct and indirect methods for the demonstration of surface Igs and describes certain physicochemical properties of isolated surface Ig molecules. Roles of these surface molecules in recognition of antigen, initiation of all differentiation, and cooperation among lymphocytes and accessory cells are discussed.

Products of the major histocompatibility complex and their relationship to the immune response

The genes of the major histocompatibility complex were first known for the part they played in transplant rejection. Recently, however, it has become clear that the products of that region have an important part to play in the control of the immune response, through their effects both on cooperative and on aggressive interactions between cells. It is now possible to guess at the mechanisms which may underly the association of some major histocompatibility antigens with disease.

Variable region (Fv) determinants on mouse lymphocytes

Antisera have been raised to the Fv fragment derived from a mouse alpha/lambda myeloma. These had different reactivities for Fv and mouse immunoglobulin and two of them appeared to detect v region framework determinants on normal mouse immunoglobulins. A large proportion of mouse lymphocytes were shown to have Fv determinants on the surface which was part of the B-lymphocyte antigen receptor. Most of the reacting cells were B lymphocytes. Fv determinants were not detected on the majority of T lymphocytes including cells with known T-helper cell activity. It is concluded that in mice, T cells do not express immunoglobulin v region framework determinants on their surface.

Binding of IgM by human T lymphocytes

Ox erythrocytes, sensitized with IgM-type rabbit antibodies, were found to form rosettes with human blood lymphocytes. Granulocytes, monocytes, and macrophages appeared to lack this property. The rosette formation could be inhibited with human IgM and its Fc fragments. IgM-binding lymphocytes were also present in cell suspensions isolated from human tonsils and thymuses and among blood lymphocytes cultured in vitro. The outcome of combined marker tests and cell separation experiments disclosed that the rosetting lymphocytes belong to the T-lymphocyte population.

An improved autoradiographic technique for the detection of antibody-forming cells

An authoradiographic technique for the detection of antibody-forming cells has been developed for the assay of anti-DNP responses. The lymphoid cell suspension to be assayed was allowed to a glass slide coated with DNP-conjugated gelatin to which the secreted antibody bound during subsequent incubation. The bound antibody and its Ig class was revealed by a second incubation using 125I-anti-immunoglobulin reagents followed by autoradiography. Studies on the sensitivity and specificity of the method are presented and its advantages over other techniques described. The technique should be readily applicable to other haptens.

Surface immunoglobulin on activated human peripheral blood thymus-derived cells

Human peripheral blood lymphocytes grown in vitro were stimulated with nonspecific mitogens and in mixed lymphocyte culture. The presence of IgM and thymus (T) surface markers on large and small lymphocytes was investigated by immunofluorescence and correlated with spontaneous rosette formation. All stimulated large lymphocytes formed spontaneous rosettes and all except pokeweed mitogen (PWM)-stimulated large lymphocytes had IgM and T markers. IgG, IgA, and light chain determinants were only detected on PWM-induced large lymphocytes. Thus, surface markers expressed on activated human lymphocytes may differ for different mitogens. IgM was always present on large cells which had the T markers, and it cannot be used to identify a lymphocyte as a bone marrow-derived (B) cell. Due to the overlap of surface markers, the classification into B and thymus-derived (T) cells ought to be restricted to functional phenomena of antibody-production or cell-mediated immunity.

Identification of a high molecular weight protein on the surface of murine thymus and thymus-dependent cells

Rabbit anti-mouse Ig reacted with mouse thymocytes resulting in the formation of caps which were shed into the medium and subsequently injected into rabbits. The antiserum from these animals (AMTP) reacted strongly with thymocytes and peripheral T cells and weakly with B cells. The antiserum did not react via the Thy-1 antigen and could be made specific for T lymphocytes by absorption with B lymphocytes. By surface labeling of lymphocytes with 125I, it could be shown that the major T lymphocyte antigen recognized by AMTP was one, or possibly two, large, single chain molecules with a molecular weight of approximately 200000. This molecule was not Ig and, furthermore, the AMTP did not react with cell surface Ig of B lymphocytes. The implications of this finding for previous reports on the existence of immunoglobulin on T lymphocytes are discussed.

[Electronmicroscopic and immunohistochemical studies on human lymphocytes]

Lymphocytes from the blood of healthy individuals and of patients suffering from CLL were investigated by electron microscopy and peroxidase-immunohistochemistry. B-lymphocytes were labelled by heterologous, peroxidase-conjugated antisera directed against the Id-determinants of their membranes. T-lymphocytes were labelled by an indirect method: specific incubation with a specific anti-T-cell-globulin from the rabbit; labelling-incubation with a peroxidase-conjugated anti-rabbit-IgG-globulin from the sheep. In addition, T-lymphocytes were identified by their ability to form rosettes with sheep erythrocytes spontaneously. The quantitative results were: about 80% T-lymphocytes and about 24% B-lymphocytes in normal persons, the opposite results in CLL. T- and B-lymphocytes were photographed electron microscopically; the number of organelles in the single cells was evaluated: lysosomes in the average are more numerous in T-lymphocytes, ergastoplasm in B-lymphocytes, mitochondria are equally distributed in both groups of cells. There is so much overlapping, however, that the single cell only with the aid of immunochemistry or rosette formation can be identified as a B- or T-cell. In both, the T- and the B-cell-series, different forms of lymphocytes can be distinguished according to the degree of cell differentiation. Some further problems, as specificity of the antisera and labelling of the cells by means of their Fc-receptor are discussed.

The detection of F(ab')2-related surface antigens on the thymocytes of children

A Fowl antiserum to human polyclonal F(ab')2 with specificities for variable region antigens of both light and heavy chains and for the constant portion of the Fd fragment bound to about 20 per cent of thymocytes from three children. Binding was completely inhibited by purified human polyclonal IgG and only partly by L chains. The fowl anti-F(ab')2 also bound to a subpopulation of peripheral blood lymphocytes which was somewhat larger than the B-cell population identified with other anti-immunoglobulin sera. Binding was detected by autoradiography and the amount of radiolabel seen on thymocytes was nearly as great as that on peripheral blood lymphocytes. As no binding to thymocytes was seen with other anti-immunoglobulin sera we propose that the fowl anti-F(ab')2 recognizes immunoglobulin or material with structural similarities which is synthesized by thymocytes but of which predominantly V region determinants are exposed on the membrane surface.

Evidence against T-cell immunoglobulin from radioimmunoassay on serum and cells from bursectomized chickens

A radioimmunoassay with a sensitivity of about 50 pg of chicken immunoglobulin (Ig) was developed and employed for the estimation of Ig in the serum and in extracts of cells from hormonally bursectomized chickens. Chickens, which were judged agammaglobulinaemic by rocket immunoelectrophoresis, had at 12 weeks of age 5-100 ng of Ig/ml of serum. The Ig concentration was decreasing with a half life of 5 days. Thymus and spleen cells from such hypogammaglobulinaemic chickens were extracted with non-ionic detergents, acid urea, or combinations of urea and detergent, and the extracts were analysed for Ig by the inhibition assay. The amount of Ig found in extracts from thymocytes corresponded to less than a hundred molecules of 7S Ig/cell with a lower value of less than five molecules/cell, while extracts of spleen cells contained Ig corresponding to 60-300 molecules of Ig/cell. The inclusion in the media of a number of protease inhibitors did not increase the recovery. Extracts of thymus and spleen cells from untreated chickens contained Ig corresponding to 10-20 X 10(3) and 50-150 X 10(3) molecules of Ig/cell respectively. The results demonstrate the profound hypogammaglobulinaemia of bursectomized chickens and question the concept of an active production of receptor Ig by bursa-independent T cells.

Fc-receptors, Ia-antigens, and immunoglobulin on normal and activated mouse T lymphocytes

Using antibody coated bovine erythrocytes we were unable to demonstrate Fc-receptors on either thymus cells or T cells prepared from lymph node cell suspensions by anti-Ig column filtration. However, if parental thymus or lymph node T cells were transferred to X-irradiated F1 hybrids, activated donor T cells recovered from the recipient's spleen (ATC-spleen) were shown to express Fc-receptors. Fc-receptors were also demonstrable on ATC-spleen prepared between strain combinations differing at the M-locus. In marked contrast, Fc-receptors were not detected on ATC recovered from thoracic duct lymph (T.TDL). This applied to (a) H-2-activated T.TDL derived from normal thymus cells, (b) H-2-activated T.TDL derived from thymus cells depleted of B cells, and (c) M-locus-activated T.TDL. Of these three populations, surface Ig (of B cell origin) was detected on a large proportion of the first but not on the second and third populations. Thus, the failure to detect Fc-receptors on any of these populations could not be attributed to blocking by adsorbed surface Ig. In addition, various T-cell populations were examined by a microcytotoxicity assay for the presence of cell surface Ia-antigens. 5--10% of the thymus cells, 20--30% of cortisone-resistant thymus cells, 60--70% of lymph node cells, and 60--80% of ATC-spleen and T.TDL showed Ia.

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.

Immunoglobulin-bearing lymphocytes of the chicken. I. Heavy chain immunoglobulin commitment and organ distribution

When purified anti-immunoglobulin light chain antibodies were used in indirect immunofluorescence or labeled with 125I for autoradiographic staining, a similar percentage of Ig-bearing lymphocytes were detected by both techniques in lymphoid cell suspensions from the thymus or blood of 8-14-week-old chickens. However, a larger proportion of Ig positive lymphocytes were detected in suspensions of bursal cells by the more sensitive autoradiographic method, suggesting a lower surface density of Ig: perhaps on newly differentiated stem cells. In thymus and spleen suspensions, the proportions of Ig positive lymphocytes carrying mu and gamma-chains were roughly equal, whereas in the B cell populations of the bursa and blood, cells carrying surface gamma-chains predominated. IgA-bearing lymphocytes were only a minor population (< 5%) in lymphocyte suspensions prepared from the thymus, bursa, blood and spleen of adult chickens, but formed almost 50% of the Ig-bearing lymphocytes in the caecal tonsils.

Biological significance of Fc receptor-bearing cells among activated T lymphocytes

Lethally irradiated mice injected with syngeneic thymocytes and immunized with protein antigens develop specific helper T cells. If injected with semiallogeneic thymocytes, such mice generate H-2 antigen-specific cytotoxic T cells. Most spleen cells from these chimeric mice possess Fc receptors. The present results demonstrate that the development of Fc-receptor-bearing cells in thymocyte-injected irradiation chimeras seemingly is due to the physiological conditions in the mice rather than to the specific immunization. As a corollary, both helper T cells and cytotoxic T cells did not have Fc receptors, at least not in their effector state. Thus, Fc receptors on T cells would seem irrelevant to their immune function.

Expression of a receptor for IgM by human T cells in vitro

The capacity of human peripheral blood lymphocytes (PBL) to bind antigen-IgG antibody (EA(IgG)) and antigen-IgM antibody (EA(IgM)) complexes was investigated using a rosette technique with ox erythrocytes coated with rabbit IgG or IgM antibody. It was found that while EA(IgG)-rosette-forming cells (RFC) were detected on PBL freshly drawn from normal individuals, EA(IgM)-RFC were present only in suspensions kept in culture for 24 h in mediá supplemented with sera containing very low or no amounts of IgM. Experiments of simultaneous detection of EA(IgG)-RFC or EA(IgM)-RFC and other membrane markers for human T or B cells together with experiments on purified T or B cell populations indicated that EA(IgG)-RFC were formed by both T and B cells, while T cells only were capable of EA(IgM) rosette formation. The specificity of the receptors for IgG and IgM was determined by studying the inhibitory capacity of purified human IgM and IgG in the rosette assay. The receptor for IgG was inhibited by IgG and not by IgM, while the reverse was true for the receptor for IgM.

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.

T- and B-cell interactions in autoimmune syndromes

We have reviewed briefly some of the individual capabilities of T and B cells and how these can be modified by interactions between the two cell lines. Evidence that T cells have their own distinct receptors for antigens, yet under certain circumstances may bind IgM or IgG produced by B cells, has been particularly emphasized. The probability that B cells, in turn, may bind the antigen receptor of T-cell origin reflects the balanced nature of an intricate communication system in which interactions between antigens, antigen receptors, and binding sites for these receptors all serve to modulate the integrated functioning of T and B cells. It is suggested that this communication system is disturbed in patients with rheumatoid arthritis; specifically, it is proposed that defective feedback activity of IgG-antigen complexes on activated T cells may exist in some patients and could result in unchecked and harmful T-cell activity in the joint. Therapeutic implications of this idea are mentioned.

Conditions for inducing T helper cells in vitro

Lymphoid cells of CBA mice were triggered to act as specific helper cells by incubation with protein antigen (usually keyhole limpet haemocyanin (KLH)) in Marbrook cultures in vitro. After optimum priming, these helper cells, at optimal numbers, stimulated B cells (from unprimed spleens) to respond to trinitrophenyl-KLH in vitro. The in vitro-induced helper cells were carrier-specific. B cell depletion before helper cell induction increased the efficiency of helper cell induction and thus provided further proof of the T-cell nature of in vitro helper cells. Heterogeneity within T helper cell precursors is suggested on the basis of differences in antigen dose requirements of precursor cells in cortisone-resistant thymocytes, spleen, or lymph nodes.

Antigen binding by non-bursa-derived chicken leukocytes

Antigen-binding peripheral blood leukocytes (PBL) from normal and bursectomized agammaglobulinemic chickens were labeled by incubation in vitro with radioiodinated antigen at 4 degrees C in the presence of sodium azide. [125I]TGAL-binding cells could be detected by autoradiography of PBL from normal, unimmunized chickens at a frequency of 1 to 4 labeled cells per 10(4) leukocytes. No [125I]TGAL-binding cells were found in PBL from bursectomized chickens, even after incubation with 25 mug/ml of labeled antigen followed by prolonged autoradiographic exposure. The binding to normal PBL was specific as judged by inhibition with unlabeled TGAL but not with unlabeled TIGAL. The binding was, furthermore, inhibited by preincubation with rabbit anti-chicken L chain antibody but unaffected by normal rabbit IgG. [125I]TIGAL was, in contrast, found to bind to PBL from both normal and bursectomized chickens at a frequency of 6 to 80 labeled cells per 10(4) leukocytes. The labeling was specific, since it was inhibited by cold TIGAL but not by cold TGAL. The binding of [125I]TIGAL to PBL from bursectomized chickens showed from none to slight inhibition on preincubation of the cells with anti-L chain antibody, whereas preincubation with normal rabbit IgG resulted in almost complete inhibition. To our knowledge this is the first demonstration of antigen binding to PBL from agammaglobulinemic chickens.

The presence of IgA on the surface of rat thoractic duct lymphocytes which contain internal IgA

The presence of lymphocytes with internal IgA among cells from rat thoracic duct lymph wdy. The number of cells detected was greater in animals kept in a convential animal house compared with those maintained under specific pathogen-free conditions. Thoracic duct lymph from B rats and adult thymectomized rats also contained cell with internal IgA. The surface Ig of the IgA-containing cells was studied using a double-labeling technique with (126I) anti-Ig to detect surface Ig, and fluorescein-conjugated anti-IgA in large amounts, but very little IgM and no surface IgG2. The surface IgA was not acquired passively.

[Quantitative 125-I-autoradiography of individual cells (author's transl)]

Iodine 125, an emitter of beta-radiation with an energy lying between that of tritium and carbon-14, is investigated for its applicability in quantitative autoradiography. Absorption and geometric factors of radiation are elucidated. From this, appropriate measuring conditions are derived. The simultaneous exposure of radioactive standard sources permits the evaluation of absolute amounts of radioactivity. Standard cells with labelled membranes are a suitable source of reference taking into account the physical properties of the isotope. Sheep red blood cells are examined for their suitability as standard cells after enzymatic radioiodination. The absolute number of antigenic substances on the surface of single cells is obtained by determining the specific activity of the labelled antibody molecules, and by measuring the silver grain densities of the cells under investigation and of the standard cells. The radioactivity per standard cell can be assessed by conventional procedures. The new method is applied to the quantification of membrane-bound immunoglobulin molecules of the IgG-type on single human lymphocytes. The determination of an immunologic saturation of the labelled antibody is essential for this purpose. On the lymphocytes of a normal person and of a patient with chronic lymphatic leukaemia quite different amounts of immunoglobulins have been evaluated.

The effect of specific cell inactivation on the cellular immune response to ferredoxin peptides

Previous studies using synthetic immunogenic molecules containing two haptenic peptides (ther NH2-terminal heptapeptide and the COOH-terminal pentapeptide of oxidized ferredoxin (O-Fd) from C. pasteurianum) have shown that both peptides individually are capable of initiating lymphocyte transformation and inhibiting migration in populations of lymphocytes from O-Fd-sensitized guinea pigs. While migration inhibition could readily be stimulated by single haptenic peptides, lymphocyte treasformation appeared to be more easily induced by molecules containing two or more haptenic peptides (these could be identical or different) (Kelly, B., Levy, J.G. and Hull, D., Eur. J. Immunol., 1973. 3:574). If lymphocyte transformation is a T cell-mediated phenomenon, these observations indicate the possibility of T cell-T cell interaction. The two haptenic peptides (designated "N" and "C") were synthesized and conjugated to succinylated bovine serum albumin (S-BSA), forming the conjugates N-S-BSA and C-S-BSA, respectively. These conjugates were labeled to high specific activity with 125iodine and were used in an "antigen suicide" procedure to treat guinea pig lymph node cell preparations previously sensitized to O-Fd and keyhole limpet hemocyanin (KLH). Cell populations exposed to either 125I-labeled C-S-BCA demonstrated decreased lymphocyte transformation in the presence of O-Fd but not in the presence of KLH. These results indicate specific cell inactivation by the radioactive peptide conjugates of those cells responsible for initiating cell transformation. Experiments performed by mixing 125I-labeled N-S-BSA-treated cells with 125I-labeled C-S-BSA-treated cells were successful in partially restoring the response to O-Fd and suggest possible synergy between N and C determinant binding cells in the cellular immune response to O-Fd. Evidence from B cell depletion studies suggests that this is a T cell-T cell interaction.

The role of thymus-derived lymphocytes in an antibody-mediated hapten-specific helper effect

The cellular basis of the antibody-mediated, hapten-specific anti-idiotype antibody response of CBA/J mice to a hapten conjugate of the BALB/c myeloma protein LPC-1 was examined. Previous studies have shown that anti-idiotype antibody is produced if the mice are given anti-2,4-dinitrophenyl (DNP) antibody and then immunized with DNP-LPC-1; immunization with DNP-LPC-1 or LPC-1 alone does not lead to the production of this antibody. In the present experiments, mice depleted of thymus-derived lymphocytes by two different techniques failed to make anti-idiotype antibody after transfer of anti-DNP antibody and immunization with DNP-LPC-1. However, thymus-deprived mice given anti-DNP antibody and reconstituted with thymus-derived spleen cells did make anti-idiotype antibody in response to DNP-LPC-1. Thymocytes could not reconstitute such mice for this response. The possible mechanisms for this hapten-specific, antibody-mediated, T cell-dependent helper effect are discussed. It is felt that such helper effects represent an alternate pathway to conventional specific T cell-mediated cooperation. Further examples of antibody-mediated helper effects which support this hypothesis are also presented.