cAMP-mediated suppression of a Th1 clone associated with an alteration of the intracellular redox environment

We have shown previously that the elevation of intracellular cAMP in antigen or anti-CD3-activated murine Th1 clones in the absence of antigen inhibits antigen-induced proliferation and the production of IL-2 by H2O2-mediated oxidation of p56lck and inhibits antigen-induced production of interferon-gamma by the induction of intracellular nitric oxide. Moreover, activated Th1 clones are resistant to cAMP-induced suppression. These results suggest that the immunosuppression of Th1 cells mediated by elevated intracellular cAMP is associated with an alteration in the intracellular oxidation/reduction environment. Here we report that the culture of an antigen or anti-CD3-activated murine Th1 clone with the adenylcyclase agonist forskolin (FSK) in the absence of antigen reduces the activity of intracellular catalase, and diminishes levels of intracellular reduced glutathione (GSH). Resting cells resistant to cAMP-induced suppression have higher intracellular GSH levels than antigen-activated cells susceptible to cAMP-induced suppression. The results provide further evidence that cAMP-induced suppression of Th1 clones is mediated by profound alterations in the intracellular redox environment and may be used to selectively inactivate Th1 cells activated by antigen.

Additional evidence that the sympathetic nervous system regulates the vessel wall release of tissue plasminogen activator

It is established that sympathetic neurons can synthesize, transport and store tissue plasminogen activator (t-PA) within axon terminals in the smooth muscle of vessel walls. Moreover, sympathetic excitations (e.g. physical and mental stress) are known to induce an acute release of t-PA into the circulation. However, relatively little is known about the nature and extent of sympathetic nervous system involvement in the release process. We inquired whether a chemical sympathectomy will alter the release of t-PA into the blood, and the intrinsic release of stored t-PA from isolated whole vessel explants. A long-term sympathectomy was induced in adult Sprague-Dawley rats by injection of guanethidine during a 5-week course. The destruction of ganglion neurons and vessel wall axons was verified immunohistochemically. t-PA release was assayed as the free activity in hind limb plasma and explant culture medium. Following sympathectomy: (i) the basal t-PA activity in plasma was 70% less than controls (2.92 +/- 1.96 versus 9.33 +/- 1.72 IU/ml; </= 0.001); (ii) the acute release from isolated vessels induced by bradykinin or phenylephrine was comparably reduced; and (iii) the greatest reductions occurred in densely innervated small vessel explants. The results provide new support for an autonomic regulation of neural t-PA release into the vessel wall matrix and blood of densely innervated thin-walled microvessels.

Differential regulation of T cell receptor-mediated Th1 cell IFN-gamma production and proliferation by divergent cAMP-mediated redox pathways

Culture of an H-2(s)-restricted, bovine myelin basic protein (BMBP)-specific murine Th1 clone with the adenyl cyclase agonist forskolin (FSK) or isobutylmethylxanthine (IBMX), an inhibitor of cAMP catabolism, before culture with anti-CD3 or BMBP and antigen-presenting cells (APC) suppressed antigen or anti-CD3-induced proliferation and production of interferon-gamma (IFN-gamma). Other H-2(s)-derived or H-2(b)-derived clones specific for BMBP or keyhole limpet hemocyanin (KLH) were similarly affected. FSK did not affect the expression of CD4 or the T cell receptor (TCR) but did diminish levels of the phosphorylated (activated) mitogen-activated protein (MAP) kinases early response kinase-1 (ERK-1) and ERK-2. Immunoblotting of lysates from an FSK-treated Th1 clone with antibodies to a carboxy-terminal epitope of p56(lck), a signal transduction enzyme upstream from ERK-1 and ERK2, did not detect p56(lck) unless the lysates were reduced prior to electrophoresis. Immunoblotting of nonreduced lysates with antibodies to an amino-terminal epitope demonstrated p56(lck) with a lower apparent molecular weight, characteristic of oxidized proteins. Reduction restored the detection of p56(lck) by anticarboxy-terminal p56(lck) and to mobilities indistinguishable from controls detected by the antiamino-terminal p56(lck). N-acetylcysteine or catalase prevented FSK-induced suppression of antigen-induced proliferation and the loss of carboxy-terminal epitopes of p56(lck). An inhibitor of cAMP-dependent protein kinase A (PKA) or nitric oxide synthase (NOS) did not affect FSK-induced inhibition of antigen-induced proliferation. In contrast, inhibitors of PKA or NOS, but not catalase, prevented FSK-induced suppression of IFN-gamma production. Moreover, immunoblots of lysates precipitated with anti-p56(lck), phosphotyrosine, or CD4 demonstrated that in FSK-treated, anti-CD3-stimulated cells, p56(lck) is not associated with CD4 zeta chain, nor is p56(lck) or zeta chain phosphorylated. In vitro kinase assays demonstrated that p56(lck) from FSK-treated cells does not have kinase activity. Taken together, the results suggest that an elevation of intracellular cAMP (in the absence of antigen) creates an oxidative environment that oxidizes and inactivates p56(lck) by an H(2)O(2)-dependent, PKA-independent mechanism and inhibits the production of IFN-gamma by an NO, PKA-dependent mechanism. Thus, antigen-induced proliferation and IFN-gamma production in a Th1 clone are controlled separately by different cAMP-dependent, redox-based mechanisms.

Blood mononuclear cells induce regulatory NK T thymocytes in anterior chamber-associated immune deviation

Injection of antigen into the anterior chamber (AC) of the eye, an immunologically privileged site, is associated with the induction of immune deviation, as evidenced by T helper cell (Th) 1 to Th2 cell polarization. We recently demonstrated that AC-associated immune deviation (ACAID) is a thymus-dependent phenomenon initiated by the formation of regulatory alpha,beta T-cell receptor-positive CD4(-) CD8(-) thymocytes (THYregs). In this study, the afferent and efferent limbs of this immunoregulatory loop were traced from peripheral blood to the thymus and then to the spleen by adoptive-transfer assays. The results demonstrate that (1) F4/80(+) CD1(+) peripheral blood mononuclear cells from mice whose ACs were injected with trinitrophenol-bovine serum albumin induce the appearance of natural killer (NK) 1.1(+) THYreg in naïve recipients within 24 h of intravenous infusion; (2) these NK THYregs induce (or generate) suppressor-effector T cells in the spleens of adoptive recipients; (3) these suppressor-effector spleen cells, but not the NK THYregs themselves, directly inhibit the expression of delayed-type hypersensitivity in sensitized recipients; and (4) peripheral blood mononuclear cells from AC-injected mice do not induce ACAID in thymectomized recipients. These results confirm our hypothesis that ACAID is a model of centrally induced dominant tolerance mediated by CD-1-dependent NK T cells of recent thymic origin. The results also provide evidence of a novel tolerance induction pathway by which blood-borne antigen-presenting cells generated by antigen injection into an immunologically privileged site transport antigen to the thymus and induce the formation and export of THYreg.

Detection of antigen-specific human serum proteins related to the T-cell receptor in infectious disease and in an immune response to milk proteins or chemicals

A monoclonal IgG2 antibody, MG3C9-1 A12, was prepared by immunization of mice with human serum Cohn Fraction III proteins enriched for TCR Ca+ proteins. MG3C9-1 A12 bound to Mr 28,000, antigen-specific TCR Ca+, beta-, and TCR Ca+, beta+ serum proteins associated with TGF-beta1, 2. The IgG2 monoclonal antibody also bound to T-lymphocyte proteins but did not bind to B lymphocyte proteins, human albumin, IgM, IgG, IgA, or TGF-beta1, 2, 3 immunogenic peptides. Monoclonal MG3C9-1 A12 detected TCR-related proteins specific for filarial extract, milk proteins, or benzoic acid in the sera of individuals with chronic or asymptomatic filariasis, milk intolerance, or sensitivity to toluene, respectively. TCR-related serum proteins were also detected intracellularly in mononuclear cells in frozen sections of ileum from a patient with milk intolerance and reactive mesenteric lymph nodes from a patient with a gastric ulcer. The results suggest that antigen-specific TCR-related serum proteins may be elevated during an immune response to oral, environmental, or infectious stimuli.

Immunological and in-vivo neurological studies on a benzoic acid-specific T cell-derived antigen-binding molecule from the serum of a toluene-sensitive patient

T-cell-derived antigen-binding molecules (TABMs) specific for benzoic acid were isolated from the serum of a toluene-sensitive patient. The resulting purified TABMs (BA-TABMs) did not contain immunoglobulin G and were associated with the cytokine transforming growth factor-beta (TGF-beta). BA-TABMs bound to benzoic acid conjugated to human serum albumin (BA-HSA), as well as to other chemicals conjugated to human serum albumin-including dinitrophenol and oxazolone. The binding of BA-TABMs to the conjugated chemicals increased the level of detectable TGF-beta, and a similar effect was observed with the unconjugated chemicals, benzoic acid and 2,4-dinitrophenol glycine. The increase in TGF-beta was critically dependent on the ratio between BA-TABMs and the conjugated or unconjugated chemicals; the increase was optimum at intermediate concentrations and absent at low and high concentrations. The authors used an established animal model in vivo and demonstrated that TGF-beta enhanced the inflammatory response induced by the release of neuropeptides from sensory nerves; this enhancement occurred in a dose-dependent manner. The BA-TABMs also enhanced this neurogenic inflammatory response in a dose-dependent manner, and this effect was blocked by anti-TGF-beta antibody. When the authors added either BA-HSA or benzoic acid, the effect of BA-TABMs on neurogenic inflammation was further enhanced at intermediate concentrations of antigen and was unaltered or reduced at higher concentrations. TABMs specific to particular chemicals, as a result of their association with cytokines (e.g., TGF-beta), may be implicated in symptom production in chemically sensitive patients.

Measurement of T-cell-derived antigen binding molecules and immunoglobulin G specific to Candida albicans mannan in sera of patients with recurrent vulvovaginal candidiasis

Immunoglobulin G (IgG) and T-cell-derived antigen binding molecules (TABM) specific to whole Candida extract and to Candida-derived mannans prepared by both the cetryltrimethylammonium bromide (CTAB) and alkaline degradation (PEAT) methods were measured in the sera of women with vulvovaginal candidiasis and controls. In the patients there were significantly higher levels of IgG to both CTAB and PEAT mannans and of TABM to CTAB mannan. TABM specific to CTAB mannan was purified from the serum of a patient with a high titer of this TABM. The purified TABM bound specifically to CTAB mannan and to other yeast and mold extracts. This TABM preparation was associated with transforming growth factor beta2 (TGF-beta2), and on specific binding to mannan there was a marked increase in the level of detectable TGF-beta2. This increase in TGF-beta2 level was critically dependent on the relative concentrations of the purified TABM and mannan, being smallest when either was in excess. The TABM specific to CTAB mannan was also shown to inhibit Candida-stimulated gamma interferon production. The results suggest that CTAB mannan-specific TABM may increase susceptibility to vulvovaginal candidiasis in association with a shift in the immune response to the Th2 type.

Sympathectomy decreases and adrenergic stimulation increases the release of tissue plasminogen activator (t-PA) from blood vessels: functional evidence for a neurologic regulation of plasmin production within vessel walls and other tissue matrices

Our recent morphologic studies indicated that peripheral nervous system (PNS) adrenergic neurons synthesize, transport, and store the serene protease, tissue plasminogen activator (t-PA) in axon terminals, many of which innervate vessel walls. Sympathoadrenal stimulation induces a surge of t-PA from vessel walls into the blood. The vascular endothelium, which constitutively secretes t-PA into blood also has long been widely assumed to be the principal source of this stress-induced release, but has not been verified as such. A neurologically regulated release from adrenergic stores could thus augment the known constitutive endothelial release. To functionally test this possibility, we quantitated the effects of guanethidine-induced systemic sympathectomy on the basal and stimulated release of t-PA from isolated vessel explants in superfused organ cultures. Moment-to-moment changes in the release rate were plotted from serial assays of the t-PA free activity. The effects of endothelial and adventitial nerve plexus ablations were also tested. Sympathectomy induced 30-50% reductions in t-PA release from both arterial and microvascular explants. An acute release induced by alpha-1 adrenergic receptor stimulations was also strongly suppressed, as were basal levels of the circulating enzyme in vivo. Adventitial and endothelial ablations from normal large vessel explants produced greater reductions than small vessel endothelial ablations. Ganglion electrical stimulation also induced an acute microvascular release in vivo. These and past morphologic findings indicate a physiological infusion of t-PA into the vessel walls, blood, and other innervated matrices by sympathetic neurons.

Clinical and immunological responses in subjects sensitive to solvents

Twenty patients proved sensitive to a 15-min exposure to 15 ppm toluene. We assessed patients neuropsychologically before and after toluene exposure, and they had impaired cognitive functioning characterized by a deterioration in short- and long-term memory and psychomotor coordination. We measured total immunoglobin G and T-cell antigen-binding molecules against an antigen prepared by conjugation of para-aminobenzoic acid to human serum albumin in 20 patients and 16 controls. There was no significant difference in the immunoglobulin G levels to the antigen in the 2 groups, but the levels of T-cell antigen-binding molecules against the para-aminobenzoic acid conjugated to human serum albumin were elevated significantly in subjects sensitive to toluene. We also found significant associations between T-cell antigen-binding molecule levels and (a) decreased performance on the STROOP (Colour Word) test, (b) a shift in focal length following toluene exposure, (c) clinical assessment of disability, and (d) longer histories of chemical exposure. The measurement of T-cell antigen-binding molecules against chemical haptens may be valuable in the assessment of patients who are sensitive to chemicals.

Production of serum immunoglobulins and T cell antigen binding molecules specific for cow's milk antigens in adults intolerant to cow's milk

The immune response to three cow's milk antigens, beta-lactoglobulin (BLG), alpha-lactalbumin (AL), and casein (CA) was studied in 15 milk-intolerant adult patients and 11 adult controls. IgG, IgE, and IgG subclasses (IgG1, IgG2, IgG3, IgG4) and T cell-derived antigen-binding molecules (TABM) specific for each antigen were measured in both groups. In the patient group, a significant elevation of total IgG and TABM against each of the milk antigens was found as well as raised levels of IgG1 to BLG and CA, IgG4 to BLG, and IgE to CA. TABM specific for BLG were isolated by affinity for BLG and found to be Mr 28,000-46,000 polypeptides functionally and physically associated with TGF-beta1 and TGF-beta2. These results indicate a Th2-type immune response to the milk antigens in milk-intolerant individuals compared with the control group which shows a pattern typical of anergy or deletion.

Functional and morphologic evidence of the presence of tissue-plasminogen activator in vascular nerves: implications for a neurologic control of vessel wall fibrinolysis and rigidity

Tissue plasminogen activator (t-PA) is expressed by hypothalamic and peripheral sympathetic neurons. The sympathetic axons that permeate artery walls have not been investigated as possible sources of intramural t-PA. The plasmin produced by such a system would locally activate both fibrinolysis and matrix metalloproteinases that regulate arterial collagen turnover. To assess this neural t-PA production, we investigated the capacity of rat cervical sympathetic ganglion neurons to synthesize and release t-PA, and the expression of the enzyme in carotid artery and the iris-choroid microvascular tissues that receive the ganglion axon distribution. Functional studies confirmed that (i) the ganglion neuron cell bodies synthesize t-PA mRNA, (ii) cultured ganglion carotid artery and iris-choroid microvascular explants predominantly release t-PA rather than urokinase, (iii) microvascular tissues release approximately 20 times more t-PA per milligram than carotid explants (which accords with the higher innervation density of small vessels), and (iv) removal of the endothelium did not cause major reductions in the t-PA release from carotid and microvascular explants. Immunolocalization studies then confirmed a strong expression of the enzyme within the ganglion axons, the carotid adventitia that receives these axons, and the predominantly sympathetic axon terminals in the iris-choroid microvasculature. These data indicate the existence of a previously undescribed system for the delivery of neural t-PA to vessel walls. The intramural production of plasmin induced by this system represents a novel principle for the regulation of arterial matrix flexibility, especially in the media of densely innervated small arteries and resistance arterioles involved in the pathogenesis of stroke, hypertension, and vascular aging. Thus, the data suggest an important new interface between neuroscience and vascular biology that merits further exploration.

Extracellular (soluble) antigen-specific T cell proteins related to the T cell receptor for antigen (sTCRr): serologic and primary amino acid sequence similarity to T cell receptor alpha chains and association with cytokines

Antigen-specific-effected immunoregulation by T lymphocytes is mediated by extracellular proteins produced by T lymphocytes. These immunoproteins bind specifically to nonprocessed antigen and either induce antigen-specific immunoregulatory T cells (tsfi) or effect regulation (tsfe). T cell proteins that bind specifically to nonprocessed antigen have ben termed "T cell antigen-binding molecules" (TABM), and by definition, tsfe and tsfi are, in part, TABM. To characterize tsfi, tsfe, and TABM and understand the relationships and function of these immunoproteins, we have combined the efforts of two laboratories to compare tsfi, tsfe, and TABM isolated by each laboratory. Data obtained in one laboratory were reproduced by the other, and all reagents prepared by each laboratory were exchanged. TABM, tsfi, and tsfe were found to express TCRCalpha epitopes but not TCRCbeta epitopes. The amino acid sequence of a tryptic peptide of a T cell hybridoma TABM specific for nitrophenylhydroxy acetate (NP) is similar to a TCRalpha chain and TCR pre-alpha chain amino acid sequence. ELISA and immunoblotting demonstrated that Mr 77,000 T cell hybrid-derived tsfi, tsfe, and TABM are noncovalently associated with Mr 15,000-16,000 interleukin-10 (IL-10). ELISA also demonstrated that tsfi and tsfe are associated with I-J. The ability of tsfi and tsfe to suppress a mixed lymphocyte reaction was prevented by anti-IL-10 or anti-I-J antibodies, suggesting that antigen-specific immunoregulatory T cell proteins function by an antigen-specific focusing of immunoregulatory cytokines.

Morphologic evidence for a preferential storage of tissue plasminogen activator (t-PA) in perivascular axons of the rat uvea

The uveal layer is thought to hold the largest stores of tissue plasminogen activator (t-PA) within the eye. However, the uveal cell types that contain and could release t-PA to contiguous tissues and fluids have not been clearly identified. In the present study the general distribution pattern of t-PA antigen in fresh rat iris and choroid tissue was determined by immunofluorescence in preliminary light microscopic (LM) cryosections. Transmission electron microscopic (TEM) immunogold localization was then used to detect specific cellular and subcellular sites of t-PA antigen. The primary antibody was rabbit anti-mouse t-PA IgG. The immunofluorescence in preliminary LM cryosections of both tissues was most intense over discrete linear and cross-sectioned structures that resembled the contours of axon bundles. This impression was strengthened when silver impregnation highlighted similar structures in separate sections of the same tissue samples. TEM immunogold labeling of thin sections then confirmed that the t-PA antigen was confined to the axoplasm of both myelinated and unmyelinated perivascular nerve fibers in both the iris and choroid. Gold particles were not observed over axonal membranes, myelin sheaths, Schwann cells, retinal pigment epithelium or vascular endothelial cells. Ultrathin TEM cryosections of the iris showed a localization of some particles over structures that resembled tubules and vesicles within the axoplasm, but not over mitochondria. The axonal location of t-PA was shown by the co-localization of t-PA with an antibody against rat neurofilaments. The typical axon morphology that enclosed the t-PA particle markers in all TEM sections also indicated an axonal location. Separate TEM sections were processed with conventional fixatives and stains to highlight the typical uveal axon morphology, which also confirmed the identity of perivascular axons as the sites of t-PA localization. Affinity of the primary antibody for rat t-PA was shown by an inhibition ELISA against rat uveal tissue extracts and by the inhibition of t-PA activity in aqueous humor. An amidolytic assay was used to quantify t-PA activity. Possible explanations for the preferential immunolocalization of t-PA antigen to the axoplasm of uveal nerve terminals and the need for additional functional studies to confirm a putative neural t-PA synthesis are discussed.

Direct thymic involvement in anterior chamber-associated immune deviation: evidence for a nondeletional mechanism of centrally induced tolerance to extrathymic antigens in adult mice

Recent reports have suggested that the dichotomy between central (thymic) and peripheral T cell tolerance is not absolute and that self-tolerance in perinatal animals may also involve the intrathymic generation and release to the periphery of Ag-specific immunoregulatory T cells. We have expanded this concept to include tolerance to non self Ags administered extrathymically to adult animals. In this study, we use the anterior chamber-associated immune deviation (ACAID) to demonstrate that central regulation of acquired peripheral tolerance can be induced in adult mice by the intraocular administration of low doses of nonself Ag. The results show that adult thymectomy prevents the inhibition of trinitrophenol (TNP)-specific delayed-type hypersensitivity, which normally occurs after injection of TNP-BSA into the anterior chamber (AC) of the eye. Thymocytes obtained from mice 1 to 3 days, but not 5 to 7 days, after AC injection of TNP-BSA or BSA alone specifically transfer inhibition of delayed-type hypersensitivity to mice primed with the homologous Ag. The latter observation, when correlated with the time of onset of ACAID, suggests that immunoregulatory T cells are formed in the thymus within 24 h and are exported to the peripheral lymphoid tissues between 2 and 5 days after AC injection of Ag. Immunomagnetic separation of thymocytes revealed that the immunoregulatory activity resides within the minor subset of CD4-, CD8-, TCR-alphabeta+ cells, previously postulated to induce fas ligand-mediated apoptosis and Th1 to Th2 immune deviation. Hence, the present study identifies ACAID as a prototypical model of centrally induced, nondeletional tolerance to extrathymic nonself Ags.

Direct thymic involvement in anterior chamber-associated immune deviation: evidence for a nondeletional mechanism of centrally induced tolerance to extrathymic antigens in adult mice

Recent reports have suggested that the dichotomy between central (thymic) and peripheral T cell tolerance is not absolute and that self-tolerance in perinatal animals may also involve the intrathymic generation and release to the periphery of Ag-specific immunoregulatory T cells. We have expanded this concept to include tolerance to non self Ags administered extrathymically to adult animals. In this study, we use the anterior chamber-associated immune deviation (ACAID) to demonstrate that central regulation of acquired peripheral tolerance can be induced in adult mice by the intraocular administration of low doses of nonself Ag. The results show that adult thymectomy prevents the inhibition of trinitrophenol (TNP)-specific delayed-type hypersensitivity, which normally occurs after injection of TNP-BSA into the anterior chamber (AC) of the eye. Thymocytes obtained from mice 1 to 3 days, but not 5 to 7 days, after AC injection of TNP-BSA or BSA alone specifically transfer inhibition of delayed-type hypersensitivity to mice primed with the homologous Ag. The latter observation, when correlated with the time of onset of ACAID, suggests that immunoregulatory T cells are formed in the thymus within 24 h and are exported to the peripheral lymphoid tissues between 2 and 5 days after AC injection of Ag. Immunomagnetic separation of thymocytes revealed that the immunoregulatory activity resides within the minor subset of CD4-, CD8-, TCR-alphabeta+ cells, previously postulated to induce fas ligand-mediated apoptosis and Th1 to Th2 immune deviation. Hence, the present study identifies ACAID as a prototypical model of centrally induced, nondeletional tolerance to extrathymic nonself Ags.

Serum TABM produced during anterior chamber-associated immune deviation passively transfers suppression of delayed-type hypersensitivity to primed mice

Injection of soluble protein antigen into the anterior chamber of the eye of primed mice induces anterior chamber-associated immune deviation (ACAID) which is manifested by suppression of delayed-type hypersensitivity (DTH) to the antigen. Recently, we found that ACAID induced in primed mice also results in a rapid rise in serum of soluble T lymphocyte-derived proteins specific for nominal antigen (TABM). Here, we demonstrate that serum TABM induced in primed mice during ACAID will transfer the suppression of DTH to mice primed to the same antigen. Sera from TNP-BSA-primed mice that received an anterior chamber injection of TNP-BSA, but not BSA alone, suppressed the DTH response to TNP when injected into other TNP-BSA-primed mice. Sera absorbed with Sepharose beads conjugated with either anti-TCR C(alpha), anti-TCR C(beta), anti-TABM or TNP-BSA did not contain TNP-specific TABM and did not transfer suppression of DTH. These results suggest that the antigen-specific, TCR C(alphabeta)+ TABM that appear in serum during ACAID are able to confer on or amplify the capacity of sensitized T cells to suppress DTH. We believe this to be the first demonstration of an in vivo immunologic function that is specifically associated with TABM produced in vivo.

Induction of Erythropoiesis by MHC-Mediated Cognate Interactions between B- and T-Cells

We have previously shown that the expression of membrane burst-promoting activity (mBPA), an erythropoietic cytokine, by B-lymphocytes is augmented by the addition of allogeneic effector cells to the B-cells. Here, we have examined immune mechanisms involved in the induction/promotion of erythropoiesis as assessed by the capacity of autologous and allogeneic peripheral blood lymphocytes to augment burst-forming unit-erythroid (BFU-E) in normal human bone marrow cells in vitro. Preincubation of mBPA-expressing human B-cells with monoclonal antibodies to major histocompatibility complex (MHC) antigens, abrogated erythropoietic activity of both autologous and allogeneic lymphocytes, suggesting that MHC antigens play a role in regulating the expression of the erythroid growth factor. Inhibition of BFU-E proliferation was also evident when antibodies to MHC class-I or class-II antigens were added directly to marrow culture. Furthermore, addition of anti-CD4 antibody to the cultures of PBL and autologous target BM cells markedly reduced erythroid proliferation induced by PBL. By contrast, anti-CD8 and control (UPC-10) monoclonal antibodies had no effect. These results provide evidence that MHC-mediated cognate interactions between T- and B-lymphocytes may participate in the control of erythropoiesis, either directly or by modulating mBPA function.

Elevation of intracellular cyclic AMP induces an anergic-like state in Th1 clones

Because elevated intracellular cAMP suppresses T cell receptor (TCR)-mediated effector activity and/or proliferation in response to antigen but does not always affect IL-2-stimulated proliferation, the effects of cAMP on a T lymphocyte response to antigen resemble antigen-induced anergy. To test the hypothesis that elevated cAMP induces anergy in T lymphocytes, we have precultured murine Th1 clones responsive to porcine myelin basic protein (PMBP) with dibutyryl cyclic AMP (dbcAMP) or forskolin and subsequently removed the dbcAMP or forskolin and measured the proliferative response of the clones to antigen and antigen-presenting cells (APC) in the presence or absence of exogenously added interleukin-2 (IL-2). Cells precultured with dbcAMP or forskolin for 3 days did not proliferate or produce IL-2 in response to antigen and APC, but did proliferate to antigen and APC in the presence of IL-2. Cells that had not been stimulated recently with antigen/APC or IL-2 were not affected by dbcAMP, while cells stimulated recently with antigen/APC and IL-2 were susceptible to the anergizing effect of dbcAMP. These observations support the hypothesis that elevation in intracellular cAMP in antigen-activated Th1 clones, prior to subsequent culture with antigen, induces a state of anergy.

Soluble extracellular antigen-specific T cell immunoproteins

Some T cells release proteins that bind specifically to antigens that have not been processed by antigen-presenting cells. These soluble immunoproteins induce or effect antigen-specific T cell functions in immunoregulation and/or hypersensitivity. After certain immunization regimens, T cell immunoproteins specific for the immunogen rise in serum, and therefore may be an antigen-specific, humoral manifestation of the activation of some T cells during an immune response. Although non-MHC (major histocompatibility complex)-associated antigen is bound, soluble antigen-specific T cell immunoproteins share variable and constant region epitopes and some amino acid sequence with the T cell receptor for antigen alpha or beta chains, and their expression depends on T cell receptor structural genes. Herein, the properties of extracellular antigen-specific T cell immunoproteins are reviewed and it is suggested that these molecules are a soluble analogue of the T cell receptor for antigen and provide an amplifying element for some T cell functions.

High-dose cyclophosphamide inhibits anterior chamber-associated immune deviation (ACAID) and the production of extracellular antigen-specific T cell proteins induced by trinitrophenylated (TNP) spleen cells

Injection of antigen into the anterior chamber (AC) of the eye induces the production of IgM and IgG1 antibodies and potentiates the appearance in serum of extracellular antigen-specific T cell proteins (TABM) that are specific for the AC-injected antigen. In contrast, delayed-type hypersensitivity (DTH) to the injected antigen is suppressed. This manifestation of anterior chamber-associated immune deviation (ACAID) is believed to be a key part of the basis of the immune privilege of the eye. Because cyclophosphamide (CY) exerts selective effects on immunoregulatory T cells and macrophages, we sought to determine its effects on the appearance in serum of TNP-specific TABM in mice following intracameral injection with TNP murine spleen cells followed by epicutaneous sensitization and challenge with picrylchloride. Injection of 200 mg/kg CY 2 days before AC injection of TNP spleen cells, sensitization, and challenge prevented the suppression of DTH and the production of TNP-specific TABM. The production of TNP-specific immunoglobulins was not affected. Injection of a low dose of 20 mg/kg CY enhanced DTH 100-300% in control animals, but did not prevent either ACAID or the production of TABM. These results provide further evidence that serum TABM may be a serologic indicator of T lymphocyte activity in ACAID and that ACAID is mediated by cells sensitive to high-dose CY.

Extravascular secretion of t-PA by the intact superfused choroid

PURPOSE

Demonstrate the continuous extravascular secretion of enzymatically active t-PA by the intact choroid.

METHODS

Enucleated rat eyes were dissected under microscopic control to prepare eyecups for superfusion in a small organ culture system. Individual preparations provided access to intact retinal, retinal pigment epithelial, or choroidal surfaces in situ. Cups were superfused with oxygenated Kreb's buffer (100 microliters/minute) at 37 degrees C and pH 7.4 while suspended in a microincubator. Released t-PA activity was measured by an amidolytic assay in 1-minute overflow samples and in cup media after flow interruptions.

RESULTS

Minimal basal secretion was detected in the overflow with the retina in place. Interruption of flow (10 minutes) produced a static accumulation of 0.10 +/- 0.01 IU/ml. With the retinal pigment epithelium in place after retinal removal, t-PA release was moderately accelerated. Removal of the retinal pigment epithelium to expose the Bruch's-choroidal surface produced the greatest acceleration. The 10-minute static level was 0.48 +/- 0.13 IU/ml. Release from the scleral shell after choroid removal was negligible. An acute burst release of t-PA activity (1.3 +/- 0.18 IU/ml) followed the infusion of bradykinin (5 to 20 microM) into choroidal cups.

CONCLUSION

Choroid appears to be the dominant source of a continuously secreted t-PA in superfused rat eyecup organ cultures. This enzymatically active t-PA is able to pass through an apparently intact Bruch's membrane but is largely impeded by an intact retinal pigment epithelium. It is also possible that retinal pigment epithelium contains inhibitors that could reduce the released t-PA activity. The authors propose that this secretory function of the uveal tissue, which has thus far not been recognized, may be a principal mechanism for the regulation of intraocular fluid circulation and matrix remodeling by plasmin in vivo.

Intracameral injection of antigen potentiates the production of antigen-specific T cell proteins in serum after the induction of delayed-type hypersensitivity

PURPOSE

To determine whether the introduction of antigen into the anterior chamber induces the production of extracellular antigen-specific T cell proteins (T cell antigen-binding molecules [TABM] specific for the antigen.

METHODS

Balb/c mice received an intracameral or subconjunctival injection of trinitrophenylated spleen cells (TNP spleen cells) before skin sensitization and challenge with picrychloride. The production of TNP-specific TABM in serum was quantified by enzyme-linked immunosorbent assay-based antigen binding and immunoblotting using a rabbit antiserum raised against a monoclonal antigen-specific T cell protein that induces suppressor T cells.

RESULTS

Intracameral, but not subconjunctival, injection of TNP spleen cells before contact sensitization increased the level of TNP-specific TABM in serum. At 2 days, TABM levels began to rise and peaked at 5 days after contact sensitization. Anterior chamber injection of TNP spleen cells alone into nonimmunized mice did not induce a detectable increase of TNP-specific TABM in serum. Mice that did not receive an intracameral TNP spleen cell injection but were made contact sensitive to TNP showed a diminished TNP-specific TABM response. Specificity of the TABM induced by intracameral-injection and sensitization for the TNP hapten was documented by showing that the induced TABM binds TNP-bovine serum antigen (BSA) but does not bind either BSA alone or azobenzenearsonate-ovalbumin and that immune sera raised against ovalbumin did not contain an increase in TNP-specific TABM. TNP-specific TABM in the sera of mice receiving an intracameral injection of TNP spleen cells, followed by contact sensitization with picrylchloride (PCl), were purified by affinity for TNP and were resolved by polyacrylamide gel electrophoresis and immunoblotting as M(r) 110,000 polypeptides.

CONCLUSIONS

Serum levels of TNP-specific TABM induced by contact sensitization alone are enhanced fourfold to fivefold when sensitization is preceded by the intracameral, but not the subconjunctival, injection of TNP spleen cells. The authors propose that besides suppression of systemic delayed type hypersensitivity, the intracameral injection of antigen into nonimmune mice may prime an increased production of TABM, which may indicate systemic activation of the immunoregulatory T cell circuit.

Increased basal levels of free plasminogen activator activity found in human aqueous humor

PURPOSE

To quantify the basal free t-PA activity in human aqueous humor.

METHODS

Human aqueous humor obtained by simplified pipette paracentesis at cataract surgery was tested for free t-PA activity in a revised 15-hour amidolytic assay using a t-PA standard curve (n = 15). Total antigenic levels of PAI-1, the principal PA inhibitor, were determined using an ELISA kit. The available PAI-1 activity was tested indirectly using anti-human PAI-1 antibody blocking before t-PA activity assay (n = 11). Plasminogen activator type was determined by anti-human t-PA and urokinase (u-PA) antibody blocking before activity assay (n = 7).

RESULTS

Free PA activity ranged widely (0.072 to 0.47 IU/ml; mean, 0.20 +/- 0.10 IU/ml) and was almost completed inactivated (> or = 89%) by antibody against human t-PA but not by the u-PA antibody. PAI-1 total antigen also ranged widely between (0.25 to 8.0 ng/ml; mean, 2.25 +/- 2.54 ng/ml). However, pretreatment of samples with PAI-1 antibody or by acidification (pH 3.2) to inactivate inhibitors did not increase t-PA activity levels.

CONCLUSIONS

A basal-free t-PA activity, which is predominantly t-PA, is present in human aqueous humor at approximately 20 times higher levels than previously found with an earlier assay. This activity is estimated to represent roughly 10% of total released t-PA antigen. PAI-1 is present in aqueous humor at levels considerably lower than reported values for plasma in a predominantly PA-complexed or inactive form.

T cell-derived antigen-specific humoral immune response. II. Further characterization of the response and the antigen binding T cell immunoproteins

Murine T lymphocyte-derived proteins which bind nominal antigen specifically (TABM) were detected in serum during a humoral immune response to bovine serum albumin. The TABM response was observed only when the adjuvants polyadenylic:polyuridylic acid complex (poly(A: U)), Freund's complete adjuvant or Titermax were used concurrently with antigen to immunize. When poly(A:U) was used, higher doses of antigen were optimal to stimulate TABM production than those required to stimulate immunoglobulin production. The binding of TABM in the serum of BSA-immunized mice to BSA in solid phase was inhibited specifically by 10-fold more BSA than that required to inhibit BSA-specific immunoglobulins suggesting that TABM have much less affinity for antigen than immunoglobulins. Immunoblotting of TABM in serum from BSA-immune mice, which bind BSA, demonstrated that these serum TABM are comprised of M(r) 110,000 polypeptides linked by disulfide bonds. Antigen-specific proteins in a lysate of an NP-specific T cell hybrid inhibited the recognition of serum TABM by anti-TABM antiserum while a lysate of a B cell hybridoma was not inhibitory, and serum TABM were adsorbed by monoclonal antibodies to TCR-C beta. These results provide more evidence that serum TABM may be a soluble analogue of the T cell receptor for antigen.

Tissue plasminogen activator activity in human aqueous humor

PURPOSE

To determine the levels of free plasminogen activator activity in human aqueous humor and to identify the type of activity (i.e., tissue-type t-PA or urokinase-type u-PA) that is responsible.

METHODS

Aqueous humor was obtained by a simplified pipette paracentesis before cataract surgery in 31 subjects, ages 57 to 93 years. Levels of plasminogen activator activity were determined using a modified 17-hour specific amidolytic assay. The type of plasminogen activator was investigated in selected samples based on its dependence on soluble fibrin, inhibition by amiloride, and specific antibody blocking. Activity-antigen ratios were compared in seven samples.

RESULTS

Plasminogen activator (PA) activity was present in all samples tested. PA activity ranged widely between 0.54 and 26.7 mIU/ml, with a mean value of 10.8 +/- 8.1 mIU/ml. Soluble fibrin, a known stimulator of tissue-type plasminogen activator (t-PA), was required in the assay system. Its absence decreased the measured activity by more than 90%. Amiloride, a known inhibitor of urokinase-type PA, had little or no effect in selected samples tested. The activity was blocked by anti-human t-PA antibodies but not by antibodies against human u-PA, further defining the type of PA responsible for the detected activity. t-PA antigen levels showed less variation among individuals than did activity levels. Antigen-activity ratios ranged between 89 and 552.

CONCLUSION

Plasminogen activator activity is present in the human aqueous humor in measurable quantities. The type of PA activity present is almost exclusively t-PA. t-PA activity varies more widely than antigen, as is the case in plasma.

Partial amino acid sequence of monoclonal extracellular antigen-specific T cell proteins

Antigen-specific molecules secreted by murine T cell hybrids (TABM) specific for 4-hydroxy 3-nitrophenyl (NP) or azobenzenearsonate (ABA) were purified from ascitic fluid by ion exchange chromatography and/or affinity for antigen. Partial amino acid sequence of reduced Mr 72,000 NP-specific polypeptides and Mr 20,000 peptides prepared by treatment of the ABA-specific immunoprotein with cyanogen bromide was obtained and a septapeptide of the NP-specific TABM shared 3/7 residues with the ABA-specific TABM. Both TABM shared residues present in 95% T cell receptor for antigen (TCR) V alpha subgroup I and 83-96% murine immunoglobulin V kappa Fr3. These results provide evidence that extracellular antigen-specific T cell proteins are soluble analogues of TCR alpha chains and belong to the immunoglobulin supergene family.

Regulatory effect of interferon-gamma and phorbol esters on the surface expression and biosynthesis of MHC class I antigens by human leukemia cells

We have used cell surface radioiodination, biosynthetic incorporation of [35S]methionine, and flow cytometry to analyze the effects of interferon gamma (IFN-gamma) and/or phorbol esters (PMA) on the turnover and expression of class I antigens of a human leukemia B cell line. Our results demonstrated that although both IFN-gamma and PMA enhance HLA expression, they act synergistically to increase by eightfold the amount of HLA polypeptides synthesized by the acute lymphoblastic leukemia cells and acted additively to augment the cell surface expression of HLA as quantified by flow cytometry. We observed a cyclic increase or decrease in the expression of class I antigens as a function of time in cell culture. IFN-gamma and/or PMA modulated this effect inducing more cells to express HLA maximally. These results suggest that there is a physiologic limit for the expression of major histocompatibility complex class I antigens.

Appearance of T lymphocyte-derived proteins specific for the immunizing antigen in serum during a humoral immune response

Some T lymphocytes produce extracellular proteins that bind nominal antigen specifically (TABM), and these proteins exhibit potent immunoregulatory activity. We have utilized an ELISA for Ag binding by Ag-specific TABM to detect and quantitate the appearance of Ag-specific TABM in murine serum during a humoral Ir to protein Ag. The TABM response was specific for the inducing Ag, stronger and more rapid during a secondary response, and temporally distinct from the appearance of Ig. The non-Ig serum TABM were bound by mAb specific for TCR-alpha chains and isolated by affinity for Ag were Mr 110,000 polypeptides. The TABM response did not occur in scid/scid mice unless the mice were reconstituted with thymocytes and thymocyte-reconstituted scid/scid mice produced TABM, but did not produce Ig. The results suggest that soluble TABM are an Ag-specific humoral manifestation of the Ir of some T lymphocytes.

Specific antigen binding by proteins secreted by an antigen-specific T cell hybrid

Antigen-specific molecules secreted by a murine T cell hybrid specific for azobenzene arsonate (ABA) were purified from ascites fluid by ion exchange chromatography and affinity for antigen. The antigen-specific proteins were purified 250 fold and were resolved predominantly as Mr 110,000 polypeptides by reduction and SDS-polyacrylamide gel electrophoresis. The ability of these molecules to bind antigen was analyzed by an ELISA using antigen-coated microtiter trays. Binding of the T cell proteins to antigen was detected with antisera specific for the proteins. Antigen binding to ABA-ovalbumin but not ovalbumin was optimal at 37 degrees C and protein derived from another T cell hybrid did not bind ABA-ovalbumin. Solid phase antigen binding was inhibited specifically by soluble ABA-ovalbumin, indicating that these T cell-derived proteins bind nominal antigen in the solid or liquid phase. It is suggested that these proteins represent a soluble, antigen specific manifestation of some T cell function.

Appearance of T lymphocyte-derived proteins specific for the immunizing antigen in serum during a humoral immune response

Some T lymphocytes produce extracellular proteins that bind nominal antigen specifically (TABM), and these proteins exhibit potent immunoregulatory activity. We have utilized an ELISA for Ag binding by Ag-specific TABM to detect and quantitate the appearance of Ag-specific TABM in murine serum during a humoral Ir to protein Ag. The TABM response was specific for the inducing Ag, stronger and more rapid during a secondary response, and temporally distinct from the appearance of Ig. The non-Ig serum TABM were bound by mAb specific for TCR-alpha chains and isolated by affinity for Ag were Mr 110,000 polypeptides. The TABM response did not occur in scid/scid mice unless the mice were reconstituted with thymocytes and thymocyte-reconstituted scid/scid mice produced TABM, but did not produce Ig. The results suggest that soluble TABM are an Ag-specific humoral manifestation of the Ir of some T lymphocytes.

T cell non-MHC-restricted antigen-binding molecules secreted or associated with the cell membrane are antigenically distinct

Some T cells produce membrane-associated or soluble molecules which bind nominal antigen specifically (TABM) and effect immunoregulation or events similar to cell-mediated hypersensitivity. We have used polyclonal antisera raised against an azobenzene arsonate (ABA)-specific TABM secreted by an ABA-specific T cell hybrid or against TNP-specific polypeptides produced by immunoregulatory T cells to identify the expression of soluble (secreted) or membrane-associated TABM. Ascites fluid or culture medium containing a T cell hybrid or T cell lines, respectively, contain TABM recognized only by an antiserum specific for the secreted T cell hybrid (ABA-specific) derived TABM. Conversely, an antiserum that recognized the TNP-specific polypeptides detected cell-membrane associated TABM but did not bind TABM secreted by the T cell hybrid or cell lines.

Inhibition of major histocompatibility complex class I antigen shedding up-regulates the surface expression of class I antigens on the lymphocyte cell surface

Interferon-gamma induces the expression of major histocompatibility complex class I and class II gene products. Moreover, the density of MHC antigens present on the lymphocyte surface is regulated by exfoliation of the plasma membrane. To probe the cellular mechanisms involved in IFN-gamma-induced alteration of MHC antigen expression, we measured the effects of IFN-gamma on the rate of MHC antigen shedding and the biosynthesis of H-2Dd. Balb/c splenic lymphocytes were surface-iodinated with 125I and incubated in the presence and absence of up to 1000 U/ml IFN-gamma, or they were metabolically labeled with [35S]methionine with or without 500 U/ml IFN-gamma. Radioiodinated or 35S-labeled H-2Dd was quantified by immunoprecipitation of H-2Dd from detergent lysates of radiolabeled cells that were incubated with the appropriate antibody for 4-20 h at 37 degrees C. Monoclonal antibody 34-5-8 was employed as a specific probe for H-2Dd. Loss of radioiodinated H-2Dd from the cell surface was diminished by 75-90% at 12 h in tests of lymphocytes continuously cultured with IFN-gamma (compared to control, p less than 0.05). In contrast, the biosynthetic rate was unaffected during the initial 10 h of incubation. The net result of these changes was the early appearance of an increase in H-2Dd on the cell surface. This result was in accordance with data obtained by phenotyping the untreated and treated cells using double-antibody staining methods and fluorescence-activated cell sorter analysis. Our results suggest that IFN-gamma induces MHC expression by initially retarding the exfoliation of MHC antigens from the lymphocyte surface. Delayed effects on MHC expression may be, on the other hand, mediated by increased antigen biosynthesis.

T cell derived proteins from normal human sera and their relationship to T cell antigen binding molecules

We have used procedures which have been developed to isolate murine T cell antigen binding molecules (TABM) in order to isolate TABM from normal human sera. To begin purification, ammonium sulfate (NH4)2SO4 was added to human serum and precipitated protein was dissolved in low salt buffer and resolved by ion-exchange chromatography on carboxymethylcellulose (CM). The most strongly CM nonadherent fraction was absorbed with anti-human albumin and anti-human immunoglobulin (Ig) antibodies conjugated to Sepharose beads. The resulting nonadsorbed 110,000, 70,000 and 45,000 Mr polypeptides were reactive in ELISA with a rabbit antiserum produced against non-Ig, anti-specific molecules of rhesus monkeys. These proteins possess alpha mobility upon immunoelectrophoresis and represent 0.02 to 0.05% of total serum protein. In addition, these proteins are bound by an antiserum made against a synthetic peptide corresponding to the J region of the TcR beta chain. We have made R28, a rabbit antiserum against these serum proteins which binds specifically to tetanus-specific polypeptides obtained from the culture supernatant of human T cell lines specific for tetanus. This antiserum also binds to proteins isolated from T cell but not B cell lines, and T cell proteins are able to inhibit the binding of R28 to the human serum polypeptides. The results suggest that the proteins isolated from normal human sera are T cell antigen binding molecules.

IFN-gamma retards the turnover of H-2Dd antigens by splenic lymphocytes

The effect of IFN-gamma on the rate of shedding and biosynthesis of H-2Dd was determined by culture of cell surface-radioiodinated BALB/c spleen cells with rIFN-gamma or spleen cells metabolically labeled with 35S-methionine in the presence of IFN-gamma. Radioiodinated or 35S-labeled H-2Dd was quantitated by immunoprecipitation of H-2Dd from detergent lysates of radiolabeled cells taken at different culture intervals. The loss of 125I-labeled H-2Dd was retarded 75 to 90% by IFN-gamma whereas the biosynthetic rate was unaffected during the first 10-h culture. The net result was a ninefold increase in newly synthesized cell-associated H-2Dd. The results were consistent with determination of the kinetics of increased expression of H-2Dd determined by immunofluorescence and suggest that an early effect of IFN-gamma on the expression of class I Ag is a retardation of catabolism leading to an increase of newly synthesized class I Ag.

IFN-gamma retards the turnover of H-2Dd antigens by splenic lymphocytes

The effect of IFN-gamma on the rate of shedding and biosynthesis of H-2Dd was determined by culture of cell surface-radioiodinated BALB/c spleen cells with rIFN-gamma or spleen cells metabolically labeled with 35S-methionine in the presence of IFN-gamma. Radioiodinated or 35S-labeled H-2Dd was quantitated by immunoprecipitation of H-2Dd from detergent lysates of radiolabeled cells taken at different culture intervals. The loss of 125I-labeled H-2Dd was retarded 75 to 90% by IFN-gamma whereas the biosynthetic rate was unaffected during the first 10-h culture. The net result was a ninefold increase in newly synthesized cell-associated H-2Dd. The results were consistent with determination of the kinetics of increased expression of H-2Dd determined by immunofluorescence and suggest that an early effect of IFN-gamma on the expression of class I Ag is a retardation of catabolism leading to an increase of newly synthesized class I Ag.

Ontogeny and expression of non-MHC-restricted T cell antigen-binding molecules by thymocytes and peripheral T cell subsets

The ontogeny of T cells which express major histocompatibility complex (MHC)-unrestricted T cell antigen-binding molecules (TABM) on the cell membrane was investigated. We used a rabbit anti-mouse TABM antiserum to investigate the expression of TABM by subsets of adult thymocytes, peripheral T cells, and thymocytes during gestation. TABM are expressed by CD4+, CD8-, CD4+, CD8+ thymocytes and single-positive thymocytes. During gestation, TABM are expressed as early as Day 16, and at birth the expression of TABM on thymocytes has reached adult levels. Data are also presented which suggest that the expression of membrane TABM (mTABM) on peripheral T cells can be upregulated during T cell activation. The results suggest that TABM are expressed by different T cell subsets and that TABM+ cells may utilize the same intrathymic developmental pathway as that of T cells which express the alpha/beta T cell receptor.

Expression of non-MHC-restricted T cell antigen-binding molecules by thymic lymphocytes

Heterologous antisera which recognize non-major histocompatibility complex (MHC)-restricted T cell antigen-binding molecules (TABM) were used to characterize the expression and structure of TABM on thymic lymphocytes. Approximately 70% of thymocytes express membrane molecules bound by anti-TABM antibodies (mTABM). Antibody activity for thymocyte TABM could be removed by adsorption to splenic T cells, but not by adsorption to splenic B cells. Similarly, adsorption of the antiserum to thymocytes or splenic T cells removed antibody activity to a purified TABM whereas adsorption with B cells had no effect. Radioiodinated thymic and splenic T cell mTABM were resolved by 2D-polyacrylamide gel electrophoresis and when reduced, both populations of mTABM migrated primarily as Mr 23,000 proteins with an isoelectric point range of 6.8-7.8. Multimers of this protein were also observed at Mr 85-97,000 and 130-150,000 on both thymocytes and splenic T cells. These data indicate that MHC-unrestricted antigen-binding molecules are expressed by a majority of thymocytes and these thymic TABM are structurally and antigenically similar to mTABM on peripheral cells. This suggests an ontogenic relationship between thymic TABM and peripheral TABM.

A monoclonal antigen-binding T cell immunoprotein: antigenic relatedness to T cell receptor beta chain FR1 V and J peptide segments: physicochemical distinctiveness from classical immunoglobulins and T cell receptor heterodimers

The monoclonal murine T cell hybridoma, 51H7D, was previously shown to bind the arsazobenzene hapten and to produce a soluble antigen-binding molecule. In this paper we characterize this antigen-binding immunoprotein for its relationship to known T cell receptors serologically, using antibodies specific for variable region framework, or joining region peptides predicted from gene sequence and by biochemical means. The 51H7D cell expresses a protein with subunit size of approximately 31,000, that reacts antigenically with affinity-purified antibodies directed against synthetic first framework and joining segment peptides, corresponding to the gene sequence of the T cell receptor beta chain, YT35. This molecule does not react with affinity-purified antibodies directed against murine immunoglobulin, framework 1 sequences of alpha and gamma T cell receptors, or with antibodies against synthetic heavy chain joining segments. The subunit of mol. wt. 31,000 can form higher aggregates, notably in the mol. wt range of 60,000-70,000, depending upon extraction conditions. The soluble form of the antigen-binding molecule bears the J beta cross-reactive determinant and occurs predominantly as a charge restricted molecular species of approximate mol. wt 60,000-70,000. The purified molecule has a blocked N-terminus, but quantitative statistical analysis of its amino acid composition indicates a closer relatedness to T cell receptor beta chains and other antigen-binding T cell products, than it has to alpha, gamma or delta TCR chains. No evidence for more than one type of polypeptide chain was found and the polymerization is not dependent upon the formation of disulfide bonds. These studies raise the possibility that antigen-binding soluble T cell molecules might belong to a new family of immunoproteins, that is related to, but distinct from, classical immunoglobulins and alpha beta or gamma delta heterodimers.

An approach to the unification of suppressor T cell circuits: a simplified assay for the induction of suppression by T cell-derived, antigen-binding molecules (T-ABM)

A system is presented in which the in vitro response to sheep red blood cells (SRBC) can be regulated using antigenic determinants coupled to SRBC and T cell-derived antigen-binding molecules (T-ABM) directed against the coupled determinants. T suppressor-inducer factors (TsiF's) are composed of two molecules, one of which is a T-ABM and one which bears I-J determinants (I-J+ molecule). Using two purified T-ABM which have not previously been shown to have in vitro activity, we produced antigen-specific TsiF's which were capable of inducing the suppression of the anti-SRBC response. Suppression was found to require both the T-ABM and the I-J+ molecule, SRBC conjugated with the antigen for which the T-ABM was specific, and a population of Ly-2+ T cells in the culture. Two monoclonal TsiF (or TsF1) were demonstrated to induce suppression of the anti-SRBC response in this system, provided the relevant antigen was coupled to the SRBC in culture. The results are discussed in terms of the general functions of T-ABM in the immune system. This model will be useful in direct, experimental comparisons of the function of T-ABM and suppressor T cell factors under study in different systems and laboratories.

Characterization of the molecules involved in thymocyte thymic epithelial cell adhesion

Cell to cell adhesion is important for mechanisms of cellular recognition, growth, and differentiation. The identification of molecules involved in these interactions is necessary in order to understand the molecular basis of these processes. We have previously described the development of two different thymic epithelial cell lines (TECS and TECL). Using an assay with radiolabeled thymocytes we found that thymocytes can adhere specifically to these thymic epithelial cells. This adhesion is trypsin sensitive, suggesting that involvement of specific cell surface proteins. In the present study we further characterize and begin identification of the molecules involved in this interaction. We found that thymocyte binding to thymic epithelial cells requires the presence of Ca2+ and Mg2+ and is mediated by a molecule greater than 10,000 MW. Also, we identified several antibodies which inhibit the adhesion of thymocytes to TECS. The membrane nature of the molecule mediating this interaction was confirmed by the ability of thymocyte membranes to block the inhibitory antibodies.

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.