Quantitation of T cell antigen-binding molecules (TABM) in the sera of nonimmunized, immunized, and desensitized mice

Heterologous antibodies to non-MHC-restricted T cell antigen-binding molecules (TABM) were used in an ELISA to detect and quantitate TABM levels in the sera of nonimmune mice and in mice immunized and/or desensitized to methylated bovine serum albumin (MBSA). TABM were detected at low levels in sera from nonimmune and immune mice. Amounts of TABM rose 300-fold in MBSA-immune mice within 12 hr of a desensitizing injection of MBSA, and rapidly returned to pre-desensitization levels. Serum TABM were purified by precipitation with 50% (NH4)2SO4 and chromatography in carboxymethylcellulose. The purified TABM were Mr 30,000 to 37,000 reduced, 72,000 nonreduced, and had a pI range of 5.5 to 7.1. A portion of the elevated TABM in desensitized mice bound MBSA specifically, whereas TABM from the sera of nonimmune/nondesensitized mice did not bind MBSA. The timing of the appearance of TABM early in desensitization suggests the possibility that they may play a role in the subsequent appearance of suppressor cells in later stages of this phenomenon. In addition, the results presented here raise the possibility that fluctuations in TABM levels might prove to be a sensitive indicator of immunoregulatory status in general.

Isolation of antigen-binding membrane molecules from an antigen-specific T-cell hybrid

Cell surface-radioiodinated proteins of a murine T-cell hybrid specific for and able to bind azobenzenearsonate were isolated by adsorption to Sepharose beads conjugated with a rabbit antiserum to murine T-cell antigen-binding molecules. These isolated proteins, Mr 72,000, were found to bind specifically azobenzenearsonate while proteins isolated in this manner from the tumor parent BW5147 did not bind azobenzenearsonate. Similar cell surface proteins were isolated by affinity for antigen and immunoprecipitated with an antiserum to T-cell antigen-binding molecules. The results suggest that antigen-binding T cells express T-cell antigen-binding molecules as membrane receptors for antigen.

Antigen-binding molecules of T-cells charge heterogeneity and structural lability

T-cell products released by immune cells during culture and which bind specifically the nominal antigens, trinitrophenol (TNP) or oxazalone, were isolated from culture media by hapten-affinity chromatography and compared by isoelectric focusing and 2D-gel analysis. These proteins and an azobenzenearsonate-specific T-cell product synthesized in vitro by translation of mRNA from an azobenzenearsonate-specific T-cell hybrid were also compared for structural lability of the polypeptides. Polyclonal T-cell antigen-binding molecules (TABM) specific for TNP or oxazalone showed marked charge heterogeneity and distinctions in isoelectric focusing in an acidic pH gradient, while the azobenzenearsonate-specific, clonal T-cell product displayed restricted focusing. All TABM studied showed dissociation of Mr 70,000 polypeptides to Mr 45,000 and 25,000 polypeptides after treatment with guanidine. The results provide further evidence for distinctions and similarities between TABM.

Comparison of altered expression of histocompatibility antigens with altered immune function in murine spleen cells treated with ultraviolet radiation and/or TPA

Previous studies in our laboratory demonstrated that several treatments that inhibited the ability of cells to stimulate the mixed lymphocyte reaction (MLR) also blocked the shedding of histocompatibility antigens and Ia antigens from murine spleen cells. In the present studies, one of these treatments, ultraviolet radiation (UV), was shown to cause an initial loss in the density of H-2K, IA, and IE antigens prior to the block in shedding observed after culture of these cells. Further analysis revealed that the UV-induced loss of antigens could be prevented by the presence of colchicine during irradiation. Biosynthetic analyses revealed the IA antigen synthesis was also inhibited in the UV-irradiated cells. Examination of the effects of a second agent, 12-0-tetradecanoylphorbol-13-acetate (TPA) on the turnover of histocompatibility antigens revealed that the biosynthesis and shedding of these antigens were accelerated by this agent. However, addition of TPA to UV-irradiated cells did not result in a reversal of the UV-induced block in biosynthesis of IA antigens. Results of immune function assays correlated with the biochemical studies: UV-irradiation inhibited the generation of the MLR, but TPA enhanced this reaction, and addition of TPA to mixed lymphocyte cultures with UV-irradiated stimulators did not reverse the UV-induced inhibition. These results suggest that, although the turnover of histocompatibility antigens may be affected by TPA and UV in an antagonistic fashion, additional factors other than the expression of histocompatibility antigens are operating in the inhibition of stimulation of an MLR by UV radiation or its enhancement by TPA.

Production and purification of monoclonal T lymphocyte antigen binding molecules (TABM)

T lymphocyte antigen binding molecules are distinct from B cell immunoglobulins. These proteins were produced by an antigen-specific T cell hybrid as monoclonal products and these cells were successfully grown as an ascites. The T cell antigen binding proteins in ascites were harvested and purified in milligram amounts. The procedure we describe should provide a valuable source of large quantities of pure T lymphocyte antigen binding molecules. This method will allow for studies into their mechanisms of function in regulation of the immune response, biochemistry and molecular biology as B cell myelomas and monoclones provided for the study of immunoglobulins.

Two-dimensional peptide mapping by polyacrylamide-gel electrophoresis with limited proteolysis in SDS

The peptide mapping method described by Cleveland, et al. (1) was improved to a two-dimensional analysis applicable to minute amounts (less than 0.5 microgram) of proteins. Radioiodinated proteins for analysis were purified by electrophoretic elution of the proteins from polyacrylamide gels into buffer containing 0.1% sodium dodecyl sulfate. The proteins were digested enzymatically in the presence of 0.1% sodium dodecyl sulfate and an excess of nonlabeled bovine serum albumin (0.2 mg/ml) relative to labeled substrate in order to attain reproducibility by maintaining a consistent substrate concentration among different samples. The peptides of these limited proteolytic products were resolved by two-dimensional polyacrylamide gel electrophoresis (isoelectric focusing followed by SDS-gels). The resulting 2D-peptide maps of murine and bovine albumin and a murine lymphocyte membrane protein, Tp100, showed excellent resolution and reproducibility.

Messenger RNA for an antigen-specific binding molecule from an antigen-specific T-cell hybrid

The T-cell hybridoma 51H7D specifically binds the hapten azobenzenearsonate (ABA). An antiserum (anti-PCIF) specific for antigenic determinants shared by antigen-binding molecules of T cells (TABM) was used to precipitate polyribosomes containing mRNA for TABM from this T-cell hybridoma. The resultant mRNA was translated in vitro. The translated product (TrP51H7D) bound specifically ABA and was bound by both anti-PCIF and anti-T-cell suppressor factor. The parent lymphoma BW5147 yielded a similar translated product with the same antiserum used to isolate specific mRNA containing polysomes. This product (TrPBW) was bound by the antiserum used but did not bind ABA. The specific translated protein from both cells had a pI of approximately equal to 5.0, and apparent molecular weight of 71,000 (reduced) or 145,000 (nonreduced). Both protein products, when treated with guanidine to break down all noncovalent bonds, revealed an elemental peptide of Mr 23,500. The cDNA made from the isolated mRNA had 600-900 bases. mRNA of this size is expected for a protein of Mr 25,000. Our data indicate that a TABM specific for ABA is composed of peptides of Mr 23,500.

Purification and characterization of TNP-specific immunoregulatory molecules produced by T cells sensitized by picrylchloride (PC1F)

T cell-derived TNP-specific factors associated with immunoregulatory activity were obtained by culture of T cells obtained from mice sensitized by skin-painting with picrylchloride. Culture medium was absorbed to TNP-Sepharose and TNP binding proteins were prepared by elution with TNP. The hapten affinity-purified proteins were characterized by size and charge and were found to be acidic 70,000 m.w. polypeptides that occur as monomers or oligomers. Oligomeric proteins interact with factors produced by mice injected with trinitrobenzenesulfonic acid to form factors that suppress specifically the ability of TNP-sensitized T cells to transfer contact sensitivity to TNP. Monomeric (no more than 70,000 m.w.) molecules do not form suppressor factors but can transfer contact sensitivity to TNP. Moreover, reduction and alkylation of oligomeric molecules inactivates their suppressor activity but causes them to be able to transfer contact sensitivity. The results suggest that T cell-derived antigen-specific molecules may have different effector functions dependent on their oligomeric state.

Affinity-purified antigen-specific products produced by T cells share epitopes recognized by heterologous antisera raised against several different antigen-specific products from T cells

Heterologous antisera to murine or rat T-cell antigen-binding molecules (T-ABM) were raised in rabbits or sheep. The T-ABM used for immunization were purified by affinity for antigen and did not bear known immunoglobulin isotypes. T-ABM and anti-T-ABM were raised in three separate laboratories. Antisera to T-ABM were exchanged and tested for binding to T-ABM in three separate laboratories. Thus antisera to at least three distinct T-ABM were tested directly for binding to T-ABM or by adsorption of biological activity. Rabbit antisera to murine trinitrophenol (TNP)-specific T-ABM or rat AgB-specific T-ABM bound both murine or rat T-ABM, indicating evolutionary conservation of T-ABM. Similar results were found with sheep antisera to murine T-ABM. In addition, all heterologous anti-T-ABM antisera used bound murine T-ABM specific for TNP, 4-hydroxy-3-nitrophenyl acetate (NP), SRBC, or T-cell membrane proteins with similar structure. Thus, there is a commonality of antigenic determinants between various T-ABM and T-cell membrane homologues which may be T-cell surface receptors for foreign antigen.

Purification and characterization of TNP-specific immunoregulatory molecules produced by T cells sensitized by picrylchloride (PC1F)

T cell-derived TNP-specific factors associated with immunoregulatory activity were obtained by culture of T cells obtained from mice sensitized by skin-painting with picrylchloride. Culture medium was absorbed to TNP-Sepharose and TNP binding proteins were prepared by elution with TNP. The hapten affinity-purified proteins were characterized by size and charge and were found to be acidic 70,000 m.w. polypeptides that occur as monomers or oligomers. Oligomeric proteins interact with factors produced by mice injected with trinitrobenzenesulfonic acid to form factors that suppress specifically the ability of TNP-sensitized T cells to transfer contact sensitivity to TNP. Monomeric (no more than 70,000 m.w.) molecules do not form suppressor factors but can transfer contact sensitivity to TNP. Moreover, reduction and alkylation of oligomeric molecules inactivates their suppressor activity but causes them to be able to transfer contact sensitivity. The results suggest that T cell-derived antigen-specific molecules may have different effector functions dependent on their oligomeric state.

Analysis of normal and neoplastic lymphocyte surface-labeled proteins by two-dimensional polyacrylamide gel electrophoresis

Normal and neoplastic murine and human lymphocytes were surface-labeled by lactoperoxidase-catalyzed radioiodination, and the cell lysates were subjected to two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) analyses, combining isoelectric focusing in the first dimension and sodium dodecyl sulfate-PAGE (SDS-PAGE) in the second dimension. 2D-PAGE autoradiogram patterns were reproducible and reflected differences in cell types. A string of spots with a Mr of 100K was tentatively identified as a new T-cell marker (Tp100) which was present in all murine and human T cells examined including human T lymphomas. Murine and human B cells displayed markers characteristic to B cells of each species with some similarities between them. Human lymphomas and murine cell lines showed markers which were absent or only weakly visible in normal cells. Thus, 2D-PAGE analysis of lymphocyte surface proteins proved to be a method useful for searching for various markers.

Heterologous antisera to Lyt-1+, 2- -derived antigen-binding factor detect a subfactor of an antigen-specific suppressor factor and cell surface proteins on Lyt-1+, 2- and Lyt-1-, 2+ T cells

Rabbits were immunized with TNP-specific Lyt-1+, 2- T cell-derived, antigen-binding proteins (PCI-F) released by T cells sensitized by skin painting with picrylchloride. The resulting antiserum (anti-PCI-F) bound to PCI-F and TNP-specific factors that suppressed delayed hypersensitivity (TSF) known to be comprised of PCI-F and Lyt-2+ -derived polypeptides released by cells sensitized by injection of trinitrobenzenesulfonic acid (TNBSF). Anti-PCI-F bound to T lymphocytes and 68,000 to 72,000 m.w. T cell surface proteins but not B cells on their surface proteins. Anti-PCI-F bound to both Lyt-1+ and Lyt-2+ T cells and surface proteins. A comparison of anti-PCI-F with anti-TSF indicates that anti-TSF contains specificity for Ly-2+ T cell-derived components of TSF and T cells not present in anti-PCI-F. The possibility of multiple isotypes of T cell receptors and antigen-binding molecules is discussed.

Heterologous antisera to Lyt-1+, 2- -derived antigen-binding factor detect a subfactor of an antigen-specific suppressor factor and cell surface proteins on Lyt-1+, 2- and Lyt-1-, 2+ T cells

Rabbits were immunized with TNP-specific Lyt-1+, 2- T cell-derived, antigen-binding proteins (PCI-F) released by T cells sensitized by skin painting with picrylchloride. The resulting antiserum (anti-PCI-F) bound to PCI-F and TNP-specific factors that suppressed delayed hypersensitivity (TSF) known to be comprised of PCI-F and Lyt-2+ -derived polypeptides released by cells sensitized by injection of trinitrobenzenesulfonic acid (TNBSF). Anti-PCI-F bound to T lymphocytes and 68,000 to 72,000 m.w. T cell surface proteins but not B cells on their surface proteins. Anti-PCI-F bound to both Lyt-1+ and Lyt-2+ T cells and surface proteins. A comparison of anti-PCI-F with anti-TSF indicates that anti-TSF contains specificity for Ly-2+ T cell-derived components of TSF and T cells not present in anti-PCI-F. The possibility of multiple isotypes of T cell receptors and antigen-binding molecules is discussed.

Properties of reticulum cell sarcomas in SJL/J mice. VIII. Prominent role of RCS cell I-A antigens in the stimulation of syngeneic T cells

While T cells from SJL and from F1 hybrids of SJL that do not express I-E antigens give strong proliferative responses to RCS, T cells from F1 hybrids expressing surface I-E do not. The nature of the stimulating antigen on the RCS cell surface was examined using monoclonal antibodies. Complete inhibition of the T-cell proliferative response was obtained with antibodies to I-A antigens, whereas antibodies to I-E antigens did not inhibit at all. This inhibition was mediated via an effect of the antibodies on the stimulating cells. Biochemical characterization of immunoprecipitated 125I-and 35S-labeled RCS antigens was performed using two-dimensional gel electrophoresis. Using this technique, I-A antigens were readily detected. However, neither Ia.7-specific antibodies nor antibodies specific for E alpha: E beta complexes precipitated any E alpha or E beta chains. Comparison of I-A antigens from RCS and normal SJL spleen cells revealed minor mobility differences in the gels, possibly due to differences in glycosylation, the significance of which needs to be further evaluated. Examination of RNA extracted from RCS, using E alpha and A alpha cDNA probes showed that RCS cells do not transcribe the E alpha gene as has been shown previously for normal H-2s cells. Furthermore, DNA from RCS cells showed a defect in the E alpha gene similar to that known to exist in normal H-2s cells. Our findings exclude the presence of E alpha on RCS cells and suggest a major role for I-A, either alone or in conjunction with another as yet unidentified cell surface antigen, in the stimulation of T cells.

Absorption of shed I-Ak and H-2Kk antigens by lymphoid cells

The fate of cell surface I-Ak and H-2Kk antigens shed by murine spleen cells in culture was studied by incubation of nonlabeled spleen cells or splenic T or B cells with culture fluids containing shed radiolabeled alloantigens. Approximately 30 to 40% of the shed alloantigens could be absorbed by syngeneic or allogeneic murine T cells, B cells, or macrophages, but not by heterologous erythrocytes of human peripheral blood lymphocytes. Absorption was dependent on temperature and lipids associated with the shed glycoproteins. Once absorbed, the alloantigens were catabolized by the absorbing cells with a half-life of approximately 4 hr. It is suggested that absorption of shed cell surface alloantigens may be a vehicle for intercellular communication in the immune system.

Detection of T cells that secrete molecules which share determinants with antigen-specific T-cell factors

A single-cell secretion assay was used to detect cells that secrete products which react with an antiserum that binds T cell antigen-binding polypeptides. The antiserum (R11), which was produced by immunization of rabbits with a murine trinitrophenyl-specific suppressor factor, reacts with T cells and their products and with a suppressor T-cell clone but not with B cells or their products. The secretory cells this antiserum detected were found to be unevenly distributed among various organs (spleen, lymph node, and thymus) and, to different degrees, in spleens of various strains of mice. In unimmunized CBA/J mice, approximately 1-3% of spleen cells secreted macromolecules precipitable by R11. The majority of the secretory cells could be removed by panning with a mixture of Ly 1 and Ly 2 antibodies but not with either antibody alone. This is consistent with the cells having low surface antigen densities as a result of being either "pre-T" cells or mature secretory cells analogous to B-lineage plasma cells. In agreement with the latter possibility was our finding that the secretory activity of cells detected with antisuppressor factor was comparable to that of Ig-secretory cells as detected with an anti-Ig antiserum. However, higher numbers of R11+ secretory cells were seen in the immunoglobulin-negative fraction of spleen cells from nude mice, which could be interpreted to favor the first possibility. In either case this study shows that the single-cell assay technique is well suited for the detection and characterization of molecules released by immunoregulatory T cells.

Characterization of T-cell surface proteins bound by heterologous antisera to antigen-specific T-cell products

Heterologous antisera specific for murine T-cell antigen-recognition molecules were prepared by immunization of rabbits with dinitrophenyl-specific murine T-cell suppressor factors that had been purified by hapten-affinity chromatography. The antisera (i) bind to antigen-specific T-cell products that differ in their antigen-recognizing specificity; (ii) absorb the specific suppressor activity in preparations containing suppressor factors; (iii) stain all Lyt2+ T cells brightly in indirect immunofluorescence examination, stain some Lyt1+ cells (with low intensity), and do not stain B cells; (iv) precipitate cell membrane proteins from T cells that bear striking structural resemblance to the antigen-specific molecules used for immunization. These results suggest that, like B cells, there is a commonality between antigen-specific effector molecules released by T cells and their membrane-associated receptors.

Regulation of murine B lymphocyte plasma membrane protein turnover and shedding

Lactoperoxidase-catalyzed cell surface radioiodination was employed to radiolabel murine splenic B-cell membrane immunoglobulins (IgM and IgD) and alloantigens encoded by the Major Histocompatibility Complex (I-Ak, I-Ek, H-2Kk, H-2Dk). The fate of the radiolabeled proteins was monitored by in vitro culture of labeled cells and isolation of labeled antigens from detergent lysates of the cells or culture fluids obtained at different times during culture. The effects of temperature, antimetabolites, colchicine, and cytochalasins on membrane protein catabolism demonstrated heterogeneity in rate, energy dependence, and cytoskeletal control of turnover suggesting that functional domains of turnover control exist in the B lymphocyte membrane.

Isolation and partial characterization of an antigen-specific T-cell factor associated with the suppression of delayed type hypersensitivity

Antigen-specific factors associated with immunosuppressive activity, released by cultured T cells from mice tolerant to the haptens trinitrophenyl, dinitrophenyl and oxazolone, were purified by hapten affinity chromatography. Their binding specificity for antigens paralleled their immunoregulatory activity. Like some immunoglobulin molecules, these factors had blocked NH2 termini and could be bound to Fc-like receptors on macrophages. However, neither immunoglobulin constant region determinants (isotypes) nor antigens encoded by the major histocompatibility complex were detected on the suppressive factors. The purified factors occurred as 68,000-dalton proteins and non-covalently linked dimers. No associated immunoglobulin light chain molecules were detected. The factors showed a marked propensity toward degradation with major breakdown products of 45,000-50,000 and 25,000-30,000 daltons. These results suggest that these molecules are the T-cell products analogous to B-cell immunoglobulin (equivalent to heavy chains) and that they may be the antigen-specific components which act in conjunction with major histocompatibility-controlled gene products to perform antigen-specific suppression.

I-Kk and H-2Kk antigens are shed as supramolecular particles in association with membrane lipids

The form of 125I-labeled membrane alloantigens (I-Ak and H-2Kk) and immunoglobulin M shed by murine splenic lymphocytes labeled by lactoperoxidase-catalyzed radioiodination was determined by gel chromatography and ultracentrifugation. I-Ak and H-2Kk antigens are shed as particles ranging in size from 3 X 10(5) to 2 X 10(6), whereas membrane IgM is shed as an individual unit consonant with its native size of 180,000. The effects of detergents on the size of shed I-Ak and H-2Kk and the coprecipitation of (3H) lipids with these proteins suggest that I-Ak and H-2Kk are shed in association with local membrane lipids as small membrane-derived vesicles, whereas membrane IgM is shed without detectable associated lipid.

I-Kk and H-2Kk antigens are shed as supramolecular particles in association with membrane lipids

The form of 125I-labeled membrane alloantigens (I-Ak and H-2Kk) and immunoglobulin M shed by murine splenic lymphocytes labeled by lactoperoxidase-catalyzed radioiodination was determined by gel chromatography and ultracentrifugation. I-Ak and H-2Kk antigens are shed as particles ranging in size from 3 X 10(5) to 2 X 10(6), whereas membrane IgM is shed as an individual unit consonant with its native size of 180,000. The effects of detergents on the size of shed I-Ak and H-2Kk and the coprecipitation of (3H) lipids with these proteins suggest that I-Ak and H-2Kk are shed in association with local membrane lipids as small membrane-derived vesicles, whereas membrane IgM is shed without detectable associated lipid.

Selective turnover and shedding of H-2K and H-2D antigens is controlled by the major histocompatibility complex. Implications for H-2-restricted recognition

Lactoperoxidase-catalyzed cell surface radioiodination and incorporation of [3H]-leucine were employed to radiolabel H-2K and H-2D antigens of murine spleen cells. The fate of H-2 antigens was monitored by in vitro culture of labeled cells and isolation of labeled antigens from detergent lysates of the cells and culture supernates obtained at different times during culture. H-2Kk antigens were found to be rapidly turned over and shed by CBA/J cells, whereas the turnover of H-2Dk antigens was extremely slow. Analysis of the membrane residence times of surface-labeled H-2K and H-2D antigens on spleen cells from various H-2-congenic and -recombinant strains demonstrated variations in the shedding rates of H-2K and H-2D antigens, which were controlled by genes mapping in the major histocompatibility complex. These variations show a striking correlation with published, genetically controlled quantitative variations in the cytotoxic response of T lymphocytes to chemically modified or virus-infected syngeneic cells.

Ia antigen turnover. II. The kinetics of biosynthesis and release of Ia alpha- and beta-chains by murine spleen cells in culture

The kinetics of biosynthesis, release, and turnover of Ia antigens were determined by 3H-leucine labeling, immunoprecipitation and SDS-PAGE analysis. Continuous incorporation and pulse-chase experiments demonstrated that the half-life of the total cell Ia pool was 8 hr, with radiolabeled Ia antigens released from the cell within 4 hr of culture initiation. Both Ia alpha- and beta-chains were released by the cells. I-A antigen turnover was more rapid than I-E antigen turnover. However, detailed comparison of I-A and I-E alpha- and beta-chain biosynthesis demonstrated that the E beta (Ae) chains were synthesized more rapidly than E alpha chains, at rates similar to A alpha- and A beta-chains. Once assembled, however, E alpha- and E beta (Ae)- chains were turned over at the same rate. This kinetic anomaly may reflect post-translational association of polypeptides coded by separate genes into complete I-E antigens.

Ia antigen turnover. II. The kinetics of biosynthesis and release of Ia alpha- and beta-chains by murine spleen cells in culture

The kinetics of biosynthesis, release, and turnover of Ia antigens were determined by 3H-leucine labeling, immunoprecipitation and SDS-PAGE analysis. Continuous incorporation and pulse-chase experiments demonstrated that the half-life of the total cell Ia pool was 8 hr, with radiolabeled Ia antigens released from the cell within 4 hr of culture initiation. Both Ia alpha- and beta-chains were released by the cells. I-A antigen turnover was more rapid than I-E antigen turnover. However, detailed comparison of I-A and I-E alpha- and beta-chain biosynthesis demonstrated that the E beta (Ae) chains were synthesized more rapidly than E alpha chains, at rates similar to A alpha- and A beta-chains. Once assembled, however, E alpha- and E beta (Ae)- chains were turned over at the same rate. This kinetic anomaly may reflect post-translational association of polypeptides coded by separate genes into complete I-E antigens.

Differential effects of colchicine and cytochalasins on the shedding of murine B cell membrane IgM and IgD

Lactoperoxidase (EC 1.11.1.7) catalyzed cell surface radioiodination was employed to monitor the fate of murine B cell membrane (mem) IgM and IgD on radiolabeled cells in short-term culture. Both mem-IgM and mem-IgD were shed from the cell surface with biphasic kinetics. The rapid phase of mem-IgD shedding was somewhat slower (half-time = 12 hr) than that of mem-IgM shedding (half-time = 7-8 hr). The effect of temperature, colchicine, and cytochalasin on the shedding of the two membrane immunoglobulin isotypes was determined. The shedding of mem-IgD was more energy dependent than that of mem-IgM and was sensitive to colchicine but not cytochalasin. Conversely, the shedding of mem-IgM was sensitive to cytochalasin but not colchicine. The results suggest that the mechanisms of shedding of mem-IgM and mem-IgD are qualitatively distinct and may be regulated by microfilaments or microtubules, respectively.

Differential radiolabelling of lymphocyte membrane alloantigens and immunoglobulins: variation of H2O2 concentration during lactoperoxidase catalyzed cell surface radio-iodination

The effect of H2O2 concentration on lactoperoxidase catalyzed cell surface radio-iodination and subsequent isolation of Murine splenic lymphocyte Ia, H-2K and Lyb-3 surface antigens and membrane immunoglobulins was studied. For most membrane polypeptides analyzed 0.3 mM H2O2 proved to be optimal for the recovery of radiolabelled antigens from detergent lysates of labelled cells by immunoprecipitation. Marked variations among surface antigens and membrane immunoglobulin polypeptide chains were observed for the iodination and recovery of these proteins above and below the optimal peroxide concentration. The results suggest that cell surface radio-iodination conditions should be standardized to the requirements of the particular membrane protein being studied. The differential iodination and recovery of discrete membrane components above and below optimal conditions may prove useful in the analysis of surface membrane protein structure and membrane association.

Turnover and shedding of Ia antigens by murine spleen cells in culture

Lactoperoxidase-catalyzed radioiodination was used to examine the metabolic fate of surface Ia antigens on murine spleen cells in culture. Ia antigens, detected predominately on splenic B lymphocytes, were lost from the cultured cells with biphasic kinetics: a 4 to 6 hr rapid phase, t 1/2 = 5 hr followed by slow release through 20 hr, t 1/2 = 30 hr. The rapid loss of Ia antigens observed was abolished by both harsh iodination conditions and nonphysiologic incubation conditions. The rapid decline in Ia activity was shown to be due to shedding of intact Ia antigens from the cell and to predominant release of IA subregion-coded proteins. Release of Ia antigens from the cell was accomplished by replacement at the cell surface, and thus reflected net membrane Ia turnover. Ia shedding was shown to be extremely temperature dependent, reflecting both a comparatively high activation enthalpy and entropy requirement for turnover.

Antigen-binding T cells: dose response and kinetic studies on the development of different subsets

We have described a number of the parameters involved in the in vitro induction of specific SRBC-binding T cells (T rosette-forming cells, T-RFC). Although T-RFC precursors pass through nylon, most of the induced cells do not; nor do detectable numbers of Ly 1+2, 3- cells bind antigen with sufficient stability to form rosettes. The ratio of Ly 2,3:Ly 1,2,3 T-RFC varies with time after immunization and with the dose of antigen used for stimulation. Relatively high or low doses of antigen selectively induce Ly 1,2,3 T-RFC. Ly 2,3 T-RFC, when they appear, follow Ly 1,2,3 T-RFC. Pretreatment of T cells with anti-Ly sera before RFC induction prevents formation by Ly2+ T-RFC. Since anti-Ly 1 treatment blocks RFC formation and since Ly 1,2,3, T-RFC always precede the appearance of Ly 2,3, T-RFC, our results suggest that some Ly 1+ cells (Ly 123 at least, but perhaps also Ly 1) may act as inducers, precursors, and/or amplifiers for Ly 2,3 RFC as they appear to do for Ly 2,3 suppressor and killer cells. Thus, our results confirm and extend the observed similarities between T-RFC and other Ly 2+ cells such as killer and suppressor cells as well as their differences from Ly 1+ helper cells.

Membrane proteins of the P388D1 macrophage cell line: isolation of membrane polypeptides that bind to the Fc portion of aggregated IgG

Lactoperoxidase-catalyzed cell surface radioiodination was employed to radiolabel membrane polypeptides of a murine macrophage cell line P388D1. Optimal conditions for radioiodination of P388D1 cells were determined and were found to differ from conditions used to label lymphoid cells. SDS-polyacrylamide gel electrophoresis of detergent soluble membrane polypeptides revealed that 9 to 10 molecular species from 1 X 10(5) to 0.15 X 10(5) daltons were labeled. Radioiodinated, Triton X-100 extracted P388D1 membrane polypeptides were subjected to affinity chromatography on aggregated IgG:Sepharose columns. Elution of the bound polypeptides and analysis by SDS-polyacrylamide gel electrophoresis revealed polypeptides with an apparent molecular size of 8 X 10(4), which possess binding affinity for the Fc portion of aggregated IgG. The 8 X 10(4) dalton membrane polypeptides do not readily aggregate, are resistant to degradation, are not composed of disulfide-linked subunits, and do not appear to contain much carbohydrate. Cellular binding characteristics paralleled the binding of soluble receptor for sieved fractions of aggregated IgG suggesting that these polypeptides may be responsible for the in situ binding of aggregated IgG to P388D1 cells.

Molecular identification of a surface structure on B cells (Lyb-3) and its relationship to B cell triggering

Lactoperoxidase-catalyzed radioiodination of cell surface proteins and immunochemical procedures are used to identify murine splenic lymphocyte membrane components bound by anti-Lyb-3 serum. This antiserum defines membrane components (Lyb-3) on a subpopulation of murine B cells that may function as a receptor for T cell signals. SDS-PAGE analysis of surface-labeled membrane components bound by anti-Lyb-3 serum demonstrated a single molecular species of 68,000 d. The polypeptides recognized by anti-Lyb-3 are not composed of disulfide-linked subunits and bear no antigenic relationship with known membrane immunoglobulins (IgM or IgD). Absorption of anti-Lyb-3 serum with the 68,000 d polypeptides removed the ability of anti-Lyb-3 serum to augment the in vivo immune response of mice to low doses of sheep erythrocytes. The latter provides formal proof that the 68,000 d polypeptide bound by anti-Lyb-3 serum is the target on the B cell membrane for the immunoenhancing activity of the antiserum.

Nylon adherent antigen-specific rosette-forming T cells

Shortly after intravenous immunization of mice with heterologous erythrocytes (RBC) antigen-specific Thy 1+ cells which form rosettes with the immunizing RBC (thymic-derived lymphocytes-forming rosettes [T-RFC]) appear in the spleen. These T-RFC are much less stable than Thy 1- RFC (non-thymic-derived [B-RFC]) although most if not all of both classes of RFC adhere to nylon. T-RFC are induced with low doses of antigen (which fail to induce B-RFC) and are inhibited by higher antigen doses which are optimal for induction of B-RFC. Pretreatment of mice with cyclophosphamide prevents the high dose inhibition of T-RFC. Although there are many parallels between the production of T-RFC and delayed-type hypersensitivity (DTH) it is unlikely that the T-RFC are essential for DTH reactions since DTH can be transferred with cells which pass through nylon, and such cells are almost totally depleted of T-RFC. Thus immunization can lead to the production of large numbers of antigen-specific T-RFC whose functional role in the immune response is unknown. However, the characteristics of the T-RFC suggest that they may play an important role in amplification of suppressor cell activity.

Immunoglobulin turnover in B lymphocyte subpopulations

"In vitro" turnover of leucine-labeled and of radioiodinated IgM has been studied with cells from various lymphoid organs of nude mice, i.e. lymph nodes, thoracic duct, spleen and bone marrow, as well as with subpopulations of B cells from spleen and bone marrow separated by free flow electrophoresis. Three types of IgM-producing lymphocytes could be distinguished by their turnover rates of IgM, by the size of the released IgM and by the capacity of the IgM molecules to be labeled by the lactoperoxidase-catalyzed radioiodination reaction and/or by incorporation of radioactive leucine. Type I cells release 7-8 S IgM rapidly (t1/2 = 1-3h); the released IGM is leucine-labeled and radioiodinated. Type II cells release 7-8 S IgM slowly (t1/2 =10-30); the released IgM is leucine labeled and radioiodinated. Type III cells release 19 S IgM rapidly (t1/2 =2-4 h); the released IgM is leucine labeled, but not radioiodinated. Lymph nodes and thoracic duct contain predominantly type II cells, bone marrow contains type I and II cells, spleen contains type I,II and III cells. It is suggested that type III cells are Ig-secreting plaque-forming plasma cells, type II cells are small, resting "memory" B cells, and type I cells may be newly formed antigen-inexperienced B cells.

Turnover of radioiodinated and of leucine-labeled immunoglobulin M in murine splenic lymphocytes

Lactoperoxidase-catalyzed radioiodination of cell surface proteins and biosynthetic incorporation of tritiated leucine were used to study the size and turnover of cell-associated immunoglobulins in splenic lymphocytes of different size from BALB/c, C3H, and nu/nu mice. Small spleen cells, separated from large cells by velocity sedimentation, showed a single slow rate of turnover (t1/2 = 10-30 h) of surface radioiodinated or leucine-labeled IgM released as the monomeric 7-8 S subunit of IgM. Mitogen-activated large B cells and nonstimulated large spleen cells, separated by velocity sedimentation, released leucine-labeled IgM in an initial rapid phase (t1/2 = 2-4 h) as 19 S IgM, and later released 7-8 S IgM slowly (t1/2 = 10-30 h). The iodination reaction changed neither the biphasic mode of turnover, nor, even at higher concentration of H2O2, the size of the actively secreted 19 S IgM. Radioiodination of mitogen-activated large cells or of unstimulated large cells labeled only the slowly released 7-8 S IgM, not the actively secreted 19 S IgM. Large cells of nonstimulated spleen, however, released radioiodinated as well as leucine-labeled IgM also rapidly (t1/2 = 1-3 h). These rapidly released IgM molecules were found to be 7-8 S IgM subunits. Our results indicate that these turnover rate and size differences of radioiodinated and of leucine-labeled IgM released from murine spleen cells are in part resulting from the differences in the methodology of labeling and are in other parts due to different small and large splenic lymphocytes releasing IgM of different size at different rates.

Surface proteins of thymus-derived lymphocytes and bone-marrow-derived lymphocytes. Selective isolation of immunoglobulin and the theta-antigen by non-ionic detergents

Accessible surface proteins of thymus-derived lymphocytes (T-cells) of normal CBA mice and bone-marrow-derived lymphocytes (B-cells) of congenitally athymic nu/nu mice were analysed. The surfaces of lymphocytes were radioiodinated by using the enzyme lactoperoxidase (EC 1.11.1.7), then solubilized either in acid-urea or in the non-ionic detergent Nonidet P-40. These lysates were then precipitated with antisera specific to either immunoglobulin or the theta-alloantigen in order to assess the presence of these surface markers. Comparable amounts of radioactivity in proteins specifically precipitable as immunoglobulin were obtained from T-lymphocytes and B-lymphocytes when the cells were disrupted by acid-urea. This immunoglobulin had mol. wt. approx. 180000 and was composed of light chains and mu-type heavy chains. When radioiodinated lymphocytes were solubilized with Nonidet P-40, 3-4% of radioiodinated high-molecular-weight protein of B-cells consisted of immunoglobulin, a result similar to that found with acid-urea extraction. However, with the detergent extraction, only 0.1% of T-cell surface protein was precipitable by anti-globulin reagents. The theta-alloantigen was isolated from CBA T-cells both by acid-urea and by detergent lysis. This protein possessed a mobility on polyacrylamide-gel electrophoresis in sodium dodecyl sulphate which was consistent with a mol. wt. of 60000. An identical component was isolated from the theta-positive thymoma WEHI 105. The theta-antigen was not isolated from B-cells by either of the extraction procedures used. These results provide further evidence that the surface membranes of normal T-cells and B-cells differ in physicochemical properties. In particular, various surface components possess differential solubilities in non-ionic or organic solvents. This observation provides an explanation for discrepant results that have appeared in the literature concerning the isolation of immunoglobulin from T-lymphocytes.

Cytophilic properties of surface immunoglobulin of thymus-derived lymphocytes

The cytophilic properties of released surface immunoglobulins of normal thymus lymphocytes and of activated thymus-derived lymphocytes (ATC) were analysed by lactoperoxidase-catalysed radioiodination in conjunction with immunological and autoradiographic techniques. Immunoglobulin from both normal T cells and ATC was cytophilic for macrophages (peritoneal exudate cells), but showed no detectable capacity to bind to either T lymphocytes or to bone-marrow-derived lymphocytes (B cells). Under the operative experimental conditions surface immunoglobulin of B cells did not show appreciable binding to macrophages. These results support the feasibility of models of collaboration between T cells and B cells which involve a soluble antigen-specific collaborative factor (T-cell Ig complexed with antigen) and show an obligatory requirement for macrophages.