T cells produce an antigen-binding factor with in vivo activity analogous to IgE antibody

Functions of Exosomes and Microbial Extracellular Vesicles in Allergy and Contact and Delayed-Type Hypersensitivity

Extracellular vesicles, such as exosomes, are newly recognized intercellular conveyors of functional molecular mechanisms. Notably, they transfer RNAs and proteins between different cells that can then participate in the complex pathogenesis of allergic and related hypersensitivity responses and disease mechanisms, as described herein. This review highlights this important new appreciation of the in vivo participation of such extracellular vesicles in the interactions between allergy-mediating cells. We take into account paracrine epigenetic exchanges mediated by surrounding stromal cells and the endocrine receipt of exosomes from distant cells via the circulation. Exosomes are natural ancient nanoparticles of life. They are made by all cells and in some form by all species down to fungi and bacteria, and are present in all fluids. Besides a new focus on their role in the transmission of genetic regulation, exosome transfer of allergens was recently shown to induce allergic inflammation. Importantly, regulatory and tolerogenic exosomes can potently inhibit allergy and hypersensitivity responses, usually acting nonspecifically, but can also proceed in an antigen-specific manner due to the coating of the exosome surface with antibodies. Deep analysis of processes mediated by exosomes should result in the development of early diagnostic biomarkers, as well as allergen-specific, preventive and therapeutic strategies. These will likely significantly diminish the risks of current allergen-specific parenteral desensitization procedures, and of the use of systemic immunosuppressive drugs. Since extracellular vesicles are physiological, they can be fashioned for the specific delivery of therapeutic molecular instructions through easily tolerated, noninvasive routes, such as oral ingestion, nasal administration, and perhaps even inhalation.

A subset of AID-dependent B-1a cells initiates hypersensitivity and pneumococcal pneumonia resistance

We propose that there is a special B-1a B cell subset ("sB-1a" cells) that mediates linked processes very early after immunization to initiate cutaneous contact sensitivity (CS), delayed-type hypersensitivity (DTH), and immune resistance to pneumococcal pneumonia. Our published data indicate that in CS and DTH, these initiating processes are required for elicitation of the delayed onset and late-occurring classical T cell-mediated responses. sB-1a cells resemble memory B2 cells, as they are stimulated within 1 h of immunization and depend on T helper cytokines-uniquely IL-4 from hepatic iNKT cells--for activation and rapid migration from the peritoneal cavity to the spleen to secrete IgM antibody (Ab) and Ab-derived free light chains (FLCs) by only 1 day after immunization. Unlike conventional B-1a (cB-1a) cell-produced IgM natural Ab, IgM Ab produced by sB-1a cells has high Ag affinity owing to immunoglobulin V-region mutations induced by activation-induced cytidine deaminase (AID). The dominant cB-1a cells are increased in immunized AID-deficient mice but do not mediate initiation, CS, or pneumonia resistance because natural Ab has relatively low Ag affinity because of unmutated germ-line V regions. In CS and DTH, sB-1a IgM Ag affinity is sufficiently high to mediate complement activation for generation of C5a that, together with vasoactive mediators such as TNF-α released by FLC-sensitized mast cells, activate local endothelium for extravascular recruitment of effector T cells. We conclude by discussing the possibility of functional sB-1 cells in humans.

From Mysterious Supernatant Entity to miRNA-150 in Antigen-Specific Exosomes: a History of Hapten-Specific T Suppressor Factor

Soon after the discovery of T suppressor cells by Gershon in 1970, it was demonstrated that one subpopulation of these lymphocytes induced by i.v. hapten injection suppresses contact sensitivity response mediated by effector CD4+ or CD8+ T cells in mice through the release of soluble T suppressor factor (TsF) that acts antigen specifically. Our experiments showed that biologically active TsF is a complex entity consisting of two subfactors, one antigen specific and other non-specific, produced by differently induced populations of cells. In following years, we found that the antigen-specific subfactor is a light chain of IgM antibody that is produced by B1a lymphocytes. However, the exact nature of non-specific part remained a mystery for about 30 years. Our current studies characterized TsF as regulatory miRNA-150 carried by T suppressor cell-derived exosomes that are antigen specific due to a surface coat of IgM antibody light chains produced by B1a cells. The present communication briefly summarizes our studies on TsF that led to discovery of regulating miRNA that acts antigen specifically to suppress immune response.

Delayed-type hypersensitivity: activation of mast cells by antigen-specific T-cell factors initiates the cascade of cellular interactions

In delayed-type hypersensitivity reactions sensitized T cells orchestrate a cascade of cellular interactions. Initiation of these responses depends on a newly recognized event, namely the release of vasoactive mediators fiom mast cells that are activated by antigen-specific T-cell-derivedfactors. Here Philip Askenase and Henk Van Loveren discuss how this event initiates a sequence of steps that lead to T-cell recruitment of effector cells; and how this event differs from activation of mast cells by IgE antibody. They also suggest that the conventional time-based separation of immediate and delayed hypersensitivity should be replaced by a classcation based on the type of antigen-specific lymphocyte - B or T-responsible for the effects of hypersensitivity.

Mast cells and nerves tickle in the tummy: implications for inflammatory bowel disease and irritable bowel syndrome

Mast cells are well known as versatile cells capable of releasing and producing a variety of inflammatory mediators upon activation and are often found in close proximity of neurons. In addition, inflammation leads to local activation of neurons resulting in the release neuropeptides, which also play an important immune modulatory role by stimulation of immune cells. In intestinal disorders like inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), the number of mast cells is known to be much higher than in the normal intestine. Moreover, both these disorders are also reported to be associated with alterations in neuropeptide content and in neural innervation. Mutual association between mast cells and enteric nerves has been demonstrated to be increased in pathophysiological conditions and contribute to spreading and amplification of the response in IBD and IBS. In this review the focus lies on studies appointed to the direct interaction between mast cells and nerves in IBD, IBS, and animal models for these disorders so far.

Murine model for non-IgE-mediated asthma

There is increasing evidence that inflammatory mechanisms other than atopy or eosinophilic inflammation may be involved in the pathogenesis of asthma. The mechanisms associated with non-atopic (non-IgE) or neutrophil-mediated asthma are poorly investigated. Non-atopic airway inflammation and hyperresponsiveness was induced in mice by skin sensitization with dinitrofluorobenzene (DNFB) followed by intra-airway challenge with dinitrobenzene sulfonic acid (DNS). Acute bronchoconstriction and mast cell activation were observed shortly after challenge. Increased levels of the major mast cell mediator, TNF-alpha, were found in the bronchoalveolar lavage fluid of DNFB-sensitized. Mast cells play a key role in the early release of TNF-alpha since mast-cell-deficient WBB6F1-W/Wv mice did not show an increase in TNF-alpha release after DNFB-sensitization and DNS challenge compared to their ++ littermates. Features of the late-phase pulmonary reaction included mononuclear and neutrophilic cell infiltration, pulmonary edema, in vitro tracheal hyperreactivity and in vivo airway hyperresponsiveness. These characteristics bear marked similarity with those observed in non-atopic asthmatic patients. Therefore, this model can be used to further study the mechanisms potentially responsible for the development of non-IgE-mediated asthma.

MD41, a novel T helper 0 clone, mediates mast-cell dependent delayed-type hypersensitivity in mice

In a previous study on mouse, we have shown that delayed-type hypersensitivity (DTH) could be classified into two types according to MC requirement. The first type of DTH could be elicited by sensitization with methylated human serum albumin (MHSA) in complete Freund's adjuvant (CFA) in both wild type and mast-cell deficient (W/Wv) mice. The second type could be elicited by MHSA in incomplete Freund's adjuvant (IFA) sensitization in wild type but not W/Wv mice. While the former was related to classic tuberculin (tbc)-type DTH, the latter appeared to be a novel mast-cell dependent DTH (MD-DTH). In order to investigate the mechanism of MD-DTH, in this study, we generated an effector T-cell clone (MD41) from lymph node cells of MHSA in IFA-sensitized mice and analysed its pattern of cytokine production. Our results from cytokine assays show that following antigen stimulation, MD41 cells produce significant amounts of the T helper 1 (Th1) cytokine interferon-gamma (IFN-gamma) as well as the Th2 cytokines interleukin (IL)-4 and IL-10. In addition, double staining for IL-4 and IFN-gamma revealed that MD41 cells produce both Th1- and Th2-type cytokines simultaneously, which suggest that MD41 represents a Th0 clone rather than a mixture of Th1 and Th2 clones. Adoptive transfer of MD41 cells into wild-type mice resulted in the development of DTH skin reactions similar to those produced by active sensitization, with very similar histological findings. However, DTH skin reactions could not be induced in W/Wv mice unless first reconstituted with normal bone marrow MC (BM-MC). Therefore, our study suggests that in conjunction with tissue MC, MD41, a less-polarized MD-DTH-derived Th0 clone, is capable of developing murine DTH to the same extent as strongly polarized Th1 cells and mediates MD-DTH rather than tbc-type DTH.

Subunits of IgM reconstitute defective contact sensitivity in B-1 cell-deficient xid mice: kappa light chains recruit T cells independent of complement

The elicitation of contact sensitivity (CS) to local skin challenge with the hapten trinitrophenyl (TNP) chloride requires an early process that is necessary for local recruitment of CS-effector T cells. This is called CS initiation and is due to the B-1 subset of B cells activated at immunization to produce circulating IgM Ab. At challenge, the IgM binds hapten Ag in a complex that locally activates C to generate C5a that aids in T cell recruitment. In this study, we present evidence that CS initiation is indeed mediated by C-activating classic IgM anti-TNP pentamer. We further demonstrate the involvement of IgM subunits derived either from hybridomas or from lymphoid cells of actively immunized mice. Thus, reduced and alkylated anti-TNP IgM also initiates CS, likely due to generated H chain-L chain dimers, as does a mixture of separated H and L chains that still could weakly bind hapten, but could not activate C. Remarkably, anti-TNP kappa L chains alone mediated CS initiation that was C-independent, but was dependent on mast cells. Thus, B-1 cell-mediated CS initiation required for T cell recruitment is due to activation of C by specific IgM pentamer, and also subunits of IgM, while kappa L chains act via another C-independent but mast cell-dependent pathway.

Topical tacrolimus and cyclosporin A differentially inhibit early and late effector phases of cutaneous delayed-type and immunoglobulin E hypersensitivity

Systemic and topical administration routes of tacrolimus and cyclosporin A (CsA) were compared in effects on early and late phases of elicited T-cell-mediated contact sensitivity (CS), and effects on early and late phases of cutaneous immunoglobulin E (IgE) antibody-mediated hypersensitivity responses in mice. Thus, both CS and IgE responses in the skin have an early mast-cell-dependent phase, and also a late inflammatory phase. We measured the effects of both immunosuppressants on both phases of the respective T cell versus IgE responses. Systemic administration of both agents completely suppressed CS and IgE late-phase responses, but failed to affect either early phase. In contrast, when topical CsA was used, low doses abolished the early phase of IgE responses, but even high doses did not inhibit the early phase of CS. Conversely, topical tacrolimus inhibited the early phase of CS more potently than the early phase of cutaneous IgE hypersensitivity responses. Thus, topical treatment was needed to inhibit the early phases and the two agents acted differentially, suggesting differing susceptibility of the early phases, that are probably due to different signalling mechanisms. These studies underscore the potential value of topical administration of these powerful immunosuppressive agents in the treatment of allergic diseases that exhibit features of early-phase mast-cell-dependent inflammation, and late inflammation due to mast cells or to T cells, such as atopic dermatitis or asthma, since the early phase is predominantly susceptible to topical application, while the last phase of both IgE and T-cell inflammation responds to systemic treatment with both agents.

Mast cells in the sheep, hedgehog and rat forebrain

The study was designed to reveal the distribution of various mast cell types in the forebrain of the adult sheep, hedgehog and rat. Based on their histochemical and immunocytochemical characteristics, mast cells were categorised as (1) connective tissue-type mast cells, staining metachromatically purple with the toluidine blue method, or pale red with the Alcian blue/safranin method, (2) mucosal-type or immature mast cells staining blue with the Alcian blue/safranin method and (3) serotonin immunopositive mast cells. All 3 types of brain mast cells in all species studied were located in both white and grey matter, often associated with intraparenchymal blood vessels. Their distribution pattern exhibited interspecies differences, while their number varied considerably not only between species but also between individuals of each species. A distributional left-right asymmetry, with more cells present on the left side, was observed in all species studied but it was most prominent in the sheep brain. In the sheep, mast cells were abundantly distributed in forebrain areas, while in the hedgehog and the rat forebrain, mast cells were less widely distributed and were relatively or substantially fewer in number respectively. A limited number of brain mast cells, in all 3 species, but primarily in the rat, were found to react both immunocytochemically to 5-HT antibody and histochemically with Alcian blue/safranin staining.

Neutrophil Defensins Induce Histamine Secretion from Mast Cells: Mechanisms of Action

Defensins are endogenous antimicrobial peptides stored in neutrophil granules. Here we report that a panel of defensins from human, rat, guinea pig, and rabbit neutrophils all have histamine-releasing activity, degranulating rat peritoneal mast cells with EC50 ranging from 70 to 2500 nM, and between 45 and 60% of the total histamine released. The EC50 for defensin-induced histamine secretion correlates with their net basic charge at neutral pH. There is no correlation between histamine release and antimicrobial potency. Degranulation induced by defensins has characteristics similar to those of activation by substance P. The maximum percent histamine release is achieved in <10 s, and it can be markedly inhibited by pertussis toxin (100 ng/ml) and by pretreatment of mast cells with neuraminidase. These properties differ from those for degranulation induced by IgE-dependent Ag stimulation and by the calcium ionophore A23187. GTPase activity, a measure of G protein activation, was induced in a membrane fraction from mast cells following treatment with defensin. Thus, neutrophil defensins are potent mast cell secretagogues that act in a manner similar to substance P and 48/80, through a rapid G protein-dependent response that is mechanistically distinct from Ag/IgE-dependent mast cell activation. Defensins may provide important pathways for communication between neutrophils and mast cells in defenses against microbial agents and in acute inflammatory responses.

Mast cell-derived histamine and tumour necrosis factor: differences between SJL/J and BALB/c inbred strains of mice

Mast cells cultured from bone marrow of BALB/c and SJL/J inbred strains of mice using IL-3 showed distinct patterns of growth and marked differences in their content of TNF-alpha and histamine. Mast cells derived from SJL/J mice grew and matured at a faster rate than those from BALB/c bone marrow. SJL/J mast cells were found to contain more than twice the amount of histamine and TNF-alpha in their granules than BALB/c-derived cells. In addition, when triggered by anti-DNP IgE antibody and specific antigen (DNP-albumin), mast cells derived from SJL/J mice released more histamine and TNF-alpha than mast cells derived from BALB/c mice. These results confirm previous observations regarding a genetic basis for mouse strain differences in mast cell growth rates, and extend previous observations to document differences in mast cell mediator contents. These results are consistent with the concept that genetically controlled differences in the numbers of central nervous system (CNS)-associated mast cells and their vasogenic mediators may play an important role in modulating oedema and inflammation in CNS trauma and diseases in mice.

Trypanosoma congolense infection in sheep: ultrastructural changes in the skin prior to development of local skin reactions

Events occurring in the skin of sheep prior to development of Trypanosoma congolense-induced local skin reactions (chancres) were studied using electron microscopy. Three days after infection, few trypanosomes were present in the dermal collagen. However, these parasites were more abundant 5 days after infection, and were also found in dermal lymphatics and in the connective tissue matrix between collagen bundles. Mast cells in the skin obtained 5 days after infection showed evidence of degranulation. These events may play a role during the induction phase of trypanosomal chancres.

LCB 2183 inhibits tracheal hyperreactivity and pulmonary inflammation in mouse airways

The pulmonary delayed-type hypersensitivity (DTH) reaction induced by picryl chloride is characterized by enhanced albumin concentration in the airway tissue in the early phase (2 h after challenge with picryl sulphonic acid). During the later phase (48 h after the challenge) enhanced tracheal reactivity to carbachol in vitro and cellular (mononuclear and polymorphonuclear leukocytes) accumulation into the airway tissue in vivo are prominent features. In this present study, the effects of a novel drug, LCB 2183, were examined in the pulmonary DTH reaction. LCB 2183 (25 mg/kg twice daily intragastric gavage) failed to inhibit the enhanced albumin accumulation in the early phase of this response. In contrast, LCB 2183 abolished the tracheal hyperreactivity and the leukocyte accumulation in the airways of picryl chloride-sensitized mice 48 h after the challenge. These results demonstrate that LCB 2183 could be effective in the treatment of airway hyperreactivity and pulmonary inflammation.

Involvement of histamine or tumor necrosis factor in early-type hypersensitivity

A novel early-type hypersensitivity (ETH) reaction, manifested as capillary congestion, increase of vasopermeability, and plasma protein leakage, can be induced within 1 h after challenge of antigen-sensitized mice. The mediators involved in ETH varied among different strains of mice. The poly(Glu60Ala30Tyr10) (GAT)-induced ETH in BALB/c mice was blocked by diphenhydramine (histamine H1 antagonist) and ketanserine (serotonin antagonist), but not by cimetidine (histamine H2 antagonist). These results indicate that both histamine and serotonin are involved, and that the histamine effect is mediated through a H1 receptor. Meanwhile, GAT-induced ETH in B6 mice was inhibited by anti-TNF alpha antibody suggesting that TNF alpha is involved. The mice can be classified into either histamine or TNF alpha type based on the pattern of mediator involved in ETH. A/J and CBA strains as well as BALB/c mice were classified as histamine type while A. TL, B10.BR, and C3H/He in addition to B6 mice were TNF alpha type. The observation that GAT-induced ETH in (BALB/c x B6)F1 mice was inhibited by both diphenhydramine and anti-TNF alpha suggests that the mediation of the actions of histamine or TNF alpha by GAT was genetically controlled and inherited as the dominant trait in (BALB/c x B6)F1 mice. ETH could be passively transferred by heat (56 degrees C, 4 h)-treated anti-GAT sera. Sera derived from the histamine type transferred ETH across the type barrier and histamine was the mediator, irrespective of the type of the recipient. However, sera derived from TNF alpha type only transferred ETH to the mice of the same TNF alpha type and TNF alpha was the mediator.

LCB 2183 inhibits the inflammation associated with oxazolone-induced contact sensitivity

LCB 2183, an anti-allergic and potential anti-asthma compound, has been investigated for its ability to inhibit contact sensitivity in the mouse. The delayed response to epicutaneous hapten challenge in this model is a classical T-cell-mediated inflammatory reaction which is dependent on an early initiation phase. Both the early and late components of oxazolone-induced contact sensitivity were inhibited by oral administration of LCB 2183 in a dose-dependent manner. The drug appears to act on the efferent limb of the response since administration before hapten challenge was effective, while administration before the initial sensitization was not. LCB 2183 acts early in the cascade of events leading to inflammation, since the initiation phase of the response was inhibited; nonetheless, an effect of the drug on the late acting inflammatory cells cannot be ruled out. In comparison with oral prednisolone, which was also able to inhibit both the early and late components of the response, LCB 2183 was less active. Sodium cromoglycate and nedocromil sodium, which are poorly absorbed from the gastrointestinal tract, were tested by intraperitoneal administration. Neither of these agents significantly altered the delayed response and only nedocromil sodium had a limited inhibitory effect on the early initiation phase. Thus, in this model, LCB 2183 demonstrated more anti-inflammatory potential and resembled prednisolone more closely than either nedocromil sodium or sodium cromoglycate. The possible relevance of these effects in relation to the inflammation which characterizes human asthma is considered.

T cell-mediated induction of airway hyperresponsiveness and altered lung functions in mice are independent of increased vascular permeability and mononuclear cell infiltration

Previously it was demonstrated that during delayed-type hypersensitivity reactions (DTH) to picryl chloride (PCl) in murine lungs, as a model for cellular IgE-independent immunity, tracheal hyperreactivity and increased pulmonary resistance are induced. In the present study it is demonstrated that after pretreatment with 5HT-2 antagonists, such as ketanserin and methysergide, DTH lung reactions to PCl in mice are suppressed. The increase in vascular permeability, detectable at 2 h after intranasal hapten challenge and probably necessary for the development of a classic DTH reaction, as was demonstrated in skin DTH models, as well as the classic late inflammatory component of lung DTH, is inhibited. However, in vitro tracheal hyperreactivity to the cholinergic receptor agonist carbachol and increased pulmonary resistance in vivo, both induced during the development of these inflammatory DTH lung reactions, are not affected by 5HT-2 receptor antagonist pretreatment. These results indicate that the actual presence of increased vascular permeability and mononuclear infiltrates is not a prerequisite for the development of changed lung functions and tracheal hyperresponsiveness. Thus in mice, serotonin-independent mechanisms that appear during T cell-dependent lung immune reactions induce airway hyperresponsiveness and increased pulmonary resistance.

Association between mast cells and the development of experimental autoimmune uveitis in different rat strains

To study the role of anterior uveal mast cells in experimental autoimmune uveitis (EAU), the mast cells in the iris and ciliary body of Lewis rats, Brown Norway (BN) rats, and their F1 hybrids (LBNF1) were quantitated in normal rats and during the induction period of EAU. The mean baseline mast cell number was 68.9 +/- 10.8 per anterior uvea for Lewis rats, 0.3 +/- 0.2 for BN rats, and 4.6 +/- 0.6 for LBNF1 rats. Detectable mast cells in the anterior uvea of S-Ag-immunized Lewis rats decreased to 60% of control at 6 days postimmunization, recovered to 80% at 10 days, and dropped again to 16% at 13 days, with disease onset around 14 days. In Lewis rats that were adoptively transferred with a uveitogenic T-lymphocyte line, a profound drop in anterior uveal mast cell numbers occurred in the eyes with early signs of EAU, 3 days after the transfer. The decrease in detectable mast cells is consistent with mast cell degranulation. The data suggest that anterior mast cells participate in the immunopathogenesis of EAU and may influence the genetic susceptibility to EAU.

Specific T-cell factor production and lymphocytes in the direct surroundings of a subcutaneous allogeneic tumor

Antigen-specific T-cell factors (TCF) play a role in the initiation of cellular immune responses. In allogeneic mouse-tumor models lymphocytes from the direct tumor surroundings of both euthymic and nude mice produce TCF. These lymphocytes produce TCF when collected already 1 day after subcutaneous (sc) injection of tumor cells. In contrast to euthymic mice, draining lymph nodes and spleen of nude mice did not contain TCF-producing lymphocytes at any stage after sc tumor cell injection. In sensitized euthymic mice TCF production by lymphocytes is significantly higher in the direct tumor surroundings than in draining lymph nodes or spleen. At 2 and 5 days after tumor cell injection, the mononuclear cell infiltrate of the tissue surrounding the tumor in euthymic mice showed low expression of Thy 1, CD3, TCR alpha beta, TCR gamma delta, CD4, CD8, and asialo GM1, whereas several lymphocytes and mast cells were positive for monoclonal antibody (mAb) 14-30 (directed against TCF). In both euthymic and nude mice, sc injected tumor cells showed apoptosis. In conclusion, the direct tumor surroundings are the first (and, for nude mice, the only) site of TCF production, sc injection of tumor cells attracts mAb 14-30-positive lymphocytes and renders mast cells positive for mAb 14-30.

IL-3 dependence of a Thy-1lo, B220+, IL-3 receptor-positive antigen-specific DTH-initiating clone

The elicitation of delayed-type hypersensitivity (DTH) reactions in mice is due to the sequential action of two different antigen-specific Thy-1+ cells. We have previously cloned the early-acting DTH-initiating cell from nude mice that were immunized and boosted by contact sensitization with oxazolone (OX). This clone WP-3.27 produces an antigen-specific factor, OX-F, that acts in an Ag-specific manner to initiate DTH. The clone was phenotyped as a Thy-1+, B220+, CD3-, CD4-, CD8- cell. In this report, we further detail the characteristics of this unusual Ag-specific DTH-initiating cell clone. By flow cytometry analysis, WP-3.27 is Thy-1lo, Lyt-1+ (CD5+), but CD3-, TCR-alpha beta-, and TCR-gamma delta-. Moreover, WP-3.27 does not express surface immunoglobulins but expresses B220 (CD45RA), and also some macrophage markers such as Mac-1, F4-80, and MHC class II after gamma-IFN treatment. Interestingly, this clone also expresses IL-3 receptors (IL-3R) and not IL-2R. In addition to the Ag-specific DTH-initiating factor, WP-3.27 constitutively produces IL-3. Inhibition of proliferation of WP-3.27 with an anti-mouse IL-3 monoclonal antibody suggests that the clone WP-3.27 is IL-3-dependent, at least partially. WP-3.27 also constitutively produces IL-1 and IL-6, but not TNF-alpha. LPS activation of the clone resulted in a net increase of IL-1, IL-6, and TNF-alpha production. Thus, this Ag-specific DTH-initiating cell clone makes a unique set of cytokines. Northern blot analysis demonstrated that clone WP-3.27 transcribes mRNA encoding IL-1, IL-3, IL-6, and TNF-alpha, but not for TNF-beta (lymphotoxin). The nature of this unusual cell, which displays characteristics of more than one cell lineage, is discussed.

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.

Induction of macrophage TNF alpha, IL-1, IL-6, and PGE2 production by DTH-initiating factors

The elicitation of delayed-type hypersensitivity (DTH) reactions in mice is due to the sequential action of two different, antigen-specific, Thy-1+ cells. We have previously cloned the early-acting DTH-initiating cell from nude mice that were immunized and boosted by contact sensitization with oxazolone (OX). This cell clone, WP-3.27, releases an antigen-specific factor (OX-F) that sensitizes mast cells such that specific antigen challenge will induce serotonin release which mediates the early phase of DTH. In normal mice contact sensitized with picryl chloride (PCl), a similar polyclonal factor (PCl-F) has a similar activity and is also known to bind to macrophages. Thus, we measured macrophage production of TNF alpha, IL-1, IL-6, and PGE2 in response to the hapten affinity-purified DTH-initiating factors OX-F and PCl-F. Both factors induced significant release of each cytokine and PGE2. The production of TNF alpha, IL-1, and IL-6 was measured by bioassays. Northern blot analysis showed rapid accumulation of cytokine mRNA (2-4 hr), while maximal production of PGE2 occurred at approximately 8 hr. These macrophage activating properties of OX-F and PCl-F were not due to contamination with LPS as determined by the low levels of LPS present in OX-F and PCl-F and by the failure of polymyxin B to inhibit factor-induced PGE2 and TNF alpha production. Also, macrophage activation was shown not to be due to the action of several lymphokines known to be produced by WP3.27. Separation of OX-F and PCl-F by preparative isoelectric focusing showed a similar pattern: there were two major peaks of PGE2-inducing activity observed for both factors (for PCl-F at pI of 2-3 and 5.0, and for OX-F at pI of 3.5-4 and 5.0), but not for a sham factor produced by WEHI-3 cells. The ability of DTH-initiating factors to rapidly induce macrophage cytokine release and PGE2 synthesis 4-6 hr later may suggest a role for these mediators during the respective early vascular and late cellular phases of inflammation in DTH.

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.

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.

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.

Suppression and contrasuppression in athymic nude mice: nude mice produce the antigen-specific component of a T suppressor factor that inhibits the late 24-hr phase of DTH but do not generate suppression nor contrasuppression of the early initiating phase of DTH

Previous studies demonstrated that the initiation of murine delayed-type hypersensitivity (DTH), as exemplified by contact sensitivity induced by picryl chloride (PCI) or oxazolone (OX), is due to antigen-specific, T cell-derived, DTH-initiating factors called, respectively, PCl-F and OX-F. These factors participate in the extravascular recruitment of CD4+, Th-1, DTH effector T cells in the elicitation of DTH. Related factors also participate, together with nonantigen binding factors derived from CD8+ T cells, to constitute an antigen-specific T cell-derived suppressor factor (TsF) that can down regulate the ability of Th-1 effector T cells to mediate DTH. Since it was shown recently that athymic nude mice can make antigen-specific, DTH-initiating T cell factors, the current study tested whether nude mice also could produce the antigen-specific component of the TsF that suppresses DTH effector T cells. We found that antigen-specific factors from nu/nu mice could complement the nonantigen-binding subfactor produced in normal mice to constitute the whole antigen-specific TsF. Additional studies showed that the successful adoptive cell transfer of DTH-initiating T cell activity from nude mice into normal mice required cyclophosphamide treatment of the recipient. In contrast, transfer of DTH-initiating cell activity from nu/+ mice did not require cyclophosphamide treatment of the recipients. We hypothesized that nude mice lacked contrasuppressor cells. Although nude mice were able to manifest the early, initiating phase of DTH, we found that there was no suppression of early DTH-initiating T cells in nude mice, compared to nu/+. Therefore the production of DTH-initiating T cell factor could be boosted in nude mice. The ability to boost DTH-initiating cells in nude mice should facilitate the development of cell lines and clones with the ability to initiate DTH.

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.

Regulation of delayed-type hypersensitivity-like responses in the mouse lung, determined with histological procedures: serotonin, T-cell suppressor-inducer factor and high antigen dose tolerance regulate the magnitude of T-cell dependent inflammatory reactions

We have studied delayed-type hypersensitivity (DTH) responses to picryl chloride (PCl) in the lungs of mice. Intranasal challenge with 0.6% picryl sulphonic acid (PSA), a water soluble form of PCl, of BALB/c mice, sensitized with PCl epicutaneously 1 week earlier, induced an accumulation of mononuclear inflammatory cells around bronchioli and blood vessels. Maximal inflammatory responses were seen 48 hr after challenge. These responses were antigen-specific, and also T-cell dependent, since athymic nude mice failed to show this reaction. A role for mast cells in the responses was studied using two strains of mast cell-deficient mice. In one of these (W/Wv) lung DTH responses to PCl were reduced severely. In the other strain (S1/S1d) the responses around vessels were decreased slightly, whereas the responses in the interstitial tissue and around bronchioli were similar to those in +/+ littermate controls. Involvement of serotonin was investigated using two serotonin receptor antagonists, i.e. methysergide and ketanserin. Treatment of mice with either of the antagonists prevented occurrence of the DTH-like reaction in the lung after intranasal antigen challenge. In the lungs of sensitized mice, significantly increased permeability was established 2 hr after antigen challenge. It was concluded that release of serotonin in the lung may provide an environment that comprises local vascular permeability and that facilitates the local recruitment and possibly the activation of DTH effector T cells, leading to subsequent attraction of mononuclear leucocytes into the lung. Immunological regulation of the DTH-like reactions in the lung was similar to that of contact sensitivity in the skin, since intravenous injection of an antigen-specific T-cell suppressor inducer factor prior to sensitization or pretreatment with a high dose of picryl sulphonic acid intravenously both resulted in reduction of the DTH-like lung histological response to picryl sulphonic acid. From these findings it was concluded that DTH-like lung responses are similar to DTH responses in the skin.

Studies of intestinal lymphoid tissue. XII. Epithelial lymphocyte and mucosal responses to rectal gluten challenge in celiac sprue

The immunopathologic, structural, and functional changes within rectal mucosa of known celiac sprue subjects were quantitated during local challenge with a peptic-tryptic digest of gluten. In the celiac sprue patients challenged with 2 g of digest, major effects occurred in lamina propria, submucosa, and local microvasculature. The lamina propria swelling was biphasic, starting 1-2 h after challenge with widespread extravascular deposition of fibrinogen, indicative of increased microvascular permeability, receding by 24 h postchallenge. A rapid fall in mast cells together with granule discharge suggested their involvement in this response. The late-phase swelling (48-72 h) was preceded by a rapid influx of neutrophils and basophils, the latter showing evidence of degranulation beyond 72 h. Reestablishment of vessel lumina, a rise in mast cells, and loss of neutrophils indicated tapering of the inflammatory cellular cascade by 96 h. Lymphocytes, first seen to enter the lamina by 2 h postchallenge, increased progressively, thereby resulting in substantial infiltration between 36 and 96 h. A marked rise in epithelial lymphocytes, maximal at 6-8 h, waned by 24 h. Volumes of surface and crypt epithelium remained constant throughout. In another challenge series with 4 g of gluten digest, electrical potential difference across rectal mucosa decreased significantly 12 h postchallenge, but the associated decreases in net sodium and chloride absorptive fluxes were insignificant. It is concluded that rectal mucosa is sensitized to gluten in celiac sprue disease and thus offers a promising and convenient in vivo substrate for investigative and diagnostic purposes.

Mast cell polymorphisms. Present concepts, future directions

Although mast cells are widely distributed in the body, their functions are poorly known. The elucidation of mast cell function is complicated by growing evidence that mast cells are heterogeneous. Recent studies of mast cell ontogeny suggest that microenvironmental stimuli control the phenotypic expression of parts of the genome leading to subtype differences in a common lineage. Mast cells influence cell proliferation, differentiation, and activation in a range of target cells, although until recently they were considered important only in immediate hypersensitivity. However, they function in delayed-type hypersensitivity, potentiate cytotoxicity of eosinophils and macrophages, and are cytotoxic for certain targets themselves. Mast cell mediators influence blood flow and vascular permeability and facilitate angiogenesis. Numerous mast cell mediators are immunoregulatory. In vitro experiments have begun to investigate the role of mast cells in fibrotic diseases. Further knowledge of mast cell heterogeneity will provide the basis for new therapies in inflammatory diseases of the intestine and other organs.

Clinical assessment of host defense

Host defense mechanisms are a determinant of infection. Anergy in surgical patients is a signal of broadly based immune deficits, which include abnormalities in specific and local nonspecific antibacterial defenses and related life-threatening sepsis. Analysis of these abnormalities and other risk factors allows us to generate a long-predictive equation of individual probability of death.

Transfer of experimental allergic encephalomyelitis to bone marrow chimeras. Endothelial cells are not a restricting element

The adoptive transfer of clinical and histopathologic signs of experimental allergic encephalomyelitis (EAE) requires MHC compatibility between cell donor and cell recipient. The results of adoptive transfer studies using F1 to parent bone marrow chimeras as recipients of parental-derived BP-sensitive spleen cells indicate that this restriction is not expressed at the level of the endothelial cell but is confined to the cells of bone marrow derivation. Furthermore, these results indicate that the development of EAE is not dependent on the activity of MHC-restricted cytotoxic cells.

Modulation of experimental retinal vasculitis using dexamethasone, cyclosporin A, and prazosin

The effects of dexamethasone, cyclosporin A and prazosin were investigated in an animal model of retinal vasculitis. Both dexamethasone and cyclosporin A reduced the clinical and pathological signs of disease when given from the day of disease onset. Prazosin, an alpha 1 adrenergic antagonist, was given during the period of disease induction and blocked fluorescein leakage from actively inflamed retinal vessels, but had little effect on the clinical and pathological signs of disease. This study demonstrates the feasibility of using this animal model for therapeutic trials of anti-inflammatory agents in retinal vasculitis. The effect of prazosin on reducing vascular leakage from retinal vessels has implications for the treatment of inflammatory macula oedema in human disease.

Mast cell participation during the elicitation of murine allergic contact hypersensitivity

In order to evaluate mast cell participation in allergic contact hypersensitivity (ACH), BALB/c mice were sensitized with 0.1% trinitrochlorobenzene (TNCB). Immediately before challenge and at 1, 1.5, 2, 4, 6, 8, 12, 24, and 48 h after challenge with 1% TNCB, groups of animals had ear thickness measured, had blood collected for histamine determinations, and had both ears removed for histologic evaluation of mast cells. The increase in ear swelling was triphasic with peak increases at 1.5 h (14.3 +/- 1.6 X 10(-2) mm; mean +/- SEM), 8 h (19.9 +/- 1.8 X 10(-2) mm), and 24 h (30.2 +/- 2.9 X 10(-2) mm). A triphasic pattern of increased serum histamine was noted at 1-4 h (117% over control levels), at 12 h (131%), and at 48 h (133%). Examination of the tissue specimens from challenged animals showed modest (1+) degranulation of mast cells between 1 and 6 h with extensive (2+) degranulation at 12 h. In addition, hypogranulated mast cells were evident between 1 and 6 h, at 24 h, and at 48 h. There were no statistically significant differences in mast cell numbers at any time. Neither platelets nor other formed elements of the blood contributed to the increased blood histamine levels. These data show that mast cells are activated in a triphasic pattern during ACH, and thus suggest both early and late roles for the mast cell and its products in the evolution of ACH.

Antigen-specific augmentation factor involved in murine delayed-type footpad reaction. IV. Effect of delayed-type hypersensitivity augmentation factor on in vitro induction of DTH

We found an antigen-specific factor capable of augmenting delayed-type hypersensitivity (DTH) in the serum of mice sensitized with heterologous erythrocytes to induce a delayed footpad reaction (DFR), or in the culture supernatant of the mixture of sensitized T cells and specific antigens. This factor (DTH augmentation factor; DAF) was confirmed to augment DTH in transferred recipients. In this paper, such an activity of DAF was further investigated using the system with in vitro induction and local transfer of DTH. DAF also augmented the primary in vitro induction of DTH, when spleen cells from mice transferred with the DAF-containing serum 12 hr previously or spleen cells incubated with the DAF-containing serum on ice for 2 hr were cultured with heterologous erythrocytes. DAF acted on the induction phase of DTH and augmented a typical DTH which was dependent on Thy-1-positive T cells. DAF showed antigen specificity, but was not assigned to conventional immunoglobulin. The activity of DAF was detected when nylon-wool nonadherent cells were incubated with DAF prior to the culture of those cells and antigens, but not detected when only nylon-wool adherent cells were incubated with DAF. Thus, DAF exerted its effect through binding to acceptor cells which were included in nylon-wool nonadherent spleen cells from normal mice.

Antigen-specific augmentation of delayed-type hypersensitivity by immune serum factor in mice: augmentation of anti-tumor cytostatic activity

A humoral factor capable of augmenting delayed-type hypersensitivity antigen specificity (DAF) is present in the serum of mice sensitized with heterologous erythrocytes to induce a delayed footpad reaction (DFR). In the present study, a similar factor was identified when xenogeneic tumor cells were used as antigens. This factor also could augment the in vitro anti-tumor cytostatic activity against homologous tumor cells, which correlated with in vivo DFR to the same tumor cells. The cytostatic activity augmented by the transfer of this factor had the following characteristics: The activity appeared in the whole peritoneal exudate cells (PEC) from serum recipients at 4 days after the antigenic challenge. Such an activity was revealed in the collaboration of plastic dish-nonadherent and -adherent PEC as the primary and final effectors, respectively. The appearance of primary effector cells for such an activity was also accelerated in spleen and lymph node cells. However, a sufficient number of macrophages were always required as the final effectors in their functional expression. These primary effectors were sensitized T lymphocytes which produced lymphokine(s) such as macrophage-activating factor(s) and which contributed to this augmented cytostatic activity through the activation of macrophages. Thus, this immune serum factor seems to exert functional expression by accelerating the generation of lymphokine-producing delayed-type T lymphocytes, which is also responsible for cytostatic anti-tumor immunity.

Immune serum from mice contact-sensitized with picryl chloride contains an antigen-specific T cell factor that transfers immediate cutaneous reactivity

This report describes an activity in serum from mice that were contact-sensitized with picryl chloride (PCl) 1 to 4 days earlier. Immune serum, when given i.v., transfers the ability to elicit an immediate hypersensitivity-like ear swelling reaction in naive recipients following local challenge with PCl. This serum activity is due to an antigen-binding T cell factor that shares some properties with IgE antibody. The activity is antigen specific, and due to an antigen-binding moiety that is heat labile (56 degrees C, 4 h). However, unlike IgE antibody the serum activity is resistant to reduction and alkylation, and is retained by columns of Sepharose beads coupled with polyclonal or monoclonal antibodies that react with antigen-specific T cell factors from other systems. These columns did not retain IgE antibody activity in our experiments. Importantly, the serum activity was not retained by columns linked with antibodies directed to mouse immunoglobulins, which do retain IgE activity. We conclude from these data that the activity in PCl immune serum is not caused by IgE antibody, and is due to the presence of the previously described antigen-specific T cell factor (PCl-factor), that can activate serotonin-containing cells, such as mast cells, to release the vasoactive amine serotonin. PCl-factor transfers the ability to elicit an immediate hypersensitivity-like reaction that is an early component of delayed-type hypersensitivity. The presence of this T cell factor in the serum of actively sensitized mice provides a means to sensitize tissues throughout the body for this required, initial, serotonin-dependent component of delayed-type hypersensitivity reactions.

Intestinal immunity and inflammation: recent progress

The previous sections illustrate that we are still defining (a) which sets of lymphoid cells are present in the intestine and which are not, (b) which sets are peculiar to the intestine, and (c) how the sets that are there function in the intestinal microenvironment. An understanding of the latter point is going to require knowledge of how these sets communicate with and regulate one another via cell surface molecules such as MHC class I and class II molecules, and via soluble mediators or lymphokines. The recent advances in various technologies make this a particularly exciting time in this field because the tools are now available to address and answer some of these basic and important questions in mucosal immunology. At the same time these advances hold great promise for our eventual understanding of chronic inflammatory diseases of the intestine. As was mentioned at the outset, the immune system has considerable power for both protection and destruction. It remains a puzzle how this latter potential is contained and controlled in the intestine of most individuals, such that they do not have inflammatory disease even in the setting of intense stimulation by substances, such as endotoxin, that are phlogistic elsewhere in the body. An answer to the question of why everyone does not have intestinal inflammation could provide new insights into the mechanisms involved in chronic intestinal inflammatory diseases. The recent advances just detailed, as well as others sure to come, suggest that it is only a matter of time before such questions are answered.

Bronchoalveolar mast cells in sarcoidosis: increased numbers and accentuation of mediator release

Bronchoalveolar lavage was carried out in 36 subjects with sarcoidosis and 20 control subjects undergoing bronchoscopy for routine diagnostic purposes. The proportion of mast cells in the lavage fluid of subjects with sarcoidosis (mean (SE) 0.84% 0.09%; p less than 0.01) when compared with that of controls (mean 0.32% (0.05%); p less than 0.01). This increase was greatest in subjects with positive gallium scans but was not correlated with the percentage recovery of lymphocytes or radiographic stage. Anti-IgE induced histamine release from the bronchoalveolar cells of 15 subjects with sarcoidosis was significantly increased at all effective doses of anti-IgE. This accentuation of histamine release was significantly greater in patients with positive gallium scans and correlated directly with the percentage recovery of lymphocytes (r = 0.7, p less than 0.005). The dose-response curve of anti-IgE induced histamine release from bronchoalveolar cells of subjects with more than 20% of lymphocytes in the lavage cell population was significantly greater than the dose-response curves of subjects with fewer than 20% of lymphocytes and of controls.

Increase in skin mast cells following chronic house dust mite exposure

Application of inhalant allergens in high concentration to the mildly abraded skin of sensitive patients with atopic dermatitis gave rise to eczematous skin responses at 48 h. These lesions, infiltrated by basophils, eosinophils and mononuclear cells, are examples of cutaneous basophil hypersensitivity. Repeated application of allergen induced an increase in skin mast cells by 6 days, the mast cell hyperplasia replacing the earlier basophil infiltration. No electron microscopic evidence of mast cell heterogeneity among the recruited cells was found.

An arthritogenic lymphokine in the rat

A type II collagen-specific arthritogenic lymphokine has been identified in the rat. Arthritogenic factor (AF) is a 65 kD protein generated in vitro by T cells from rats with collagen arthritis, and it induces an erosive, proliferative synovitis when injected into the knee joint of syngeneic naive recipients. Complement does not appear to be required. These data identify a potential T cell-mediated effector mechanism in this model, and suggest that AF may function in other inflammatory synovial diseases.

Neural modulation of immune function

In this report we review our hypotheses and approaches to the study of the relationship between the central nervous and immune systems. Discussed are results pertaining to the modulation of immune parameters resulting from perturbations of the brain employing electrolytic lesions and the neuroleptic 6-hydroxydopamine. Experiments describing the central and peripheral effects of serotonin on in vivo and in vitro immune responses are also discussed.

I-A region genetic restriction in the production and action of an antigen-specific T-helper factor which bears I-A region determinant(s)

Antigen-specific T-helper factor (ThF) augments the contact sensitivity reaction induced by the injection of small numbers of picrylated cells into mice. ThF was produced by injected picrylated spleen cells into the footpads and taking the 24-hr culture supernatant of the regional lymph node cells. Analysis showed that there was a genetic restriction in the induction of ThF, between these picrylated cells and the mouse making the ThF, which maps to the I-A region. This finding suggests that the receptor on the T cell which makes ThF, and by implication ThF itself, bears recognition site(s) for both antigen and I-A. ThF was then prepared from mice painted on the skin with picryl chloride, and the genetic restriction in its action was investigated. There was a requirement for genetic matching between the mouse producing the ThF and the final recipient which mapped to the I-A region. The genotype of the picrylated cell used as a source of antigen was unimportant. This I-A genetic restriction, together with the finding that ThF bears at least some I-A determinants, suggests that ThF may act by binding to the picrylated cells used as a source of antigen through its antigen-binding site and hence provide the I-A determinants needed for the recognition of antigen in the context of self-MHC. The present findings add to the list of antigen-specific factors which have a two-chain structure and show genetic restriction in their induction, action, and in the interaction between their chains which maps to the same region as the MHC-related determinant(s) which they bear.