Superantigenic staphylococcal exotoxins induce T-cell proliferation in the presence of Langerhans cells or class II-bearing keratinocytes and stimulate keratinocytes to produce T-cell-activating cytokines

Modulation of cytokine production from an EpiOcular corneal cell culture model in response to Staphylococcus aureus superantigen

The present study investigated the hypothesis that Staphylococcus aureus enterotoxin B (SEB) produces epithelial cell death and releases inflammatory cytokines that produce stromal infiltration during contact lens induced peripheral ulceration. Epithelial cells were incubated with different doses of SEB for various time periods. Culture supernatants were assayed for cytokines IL-1 beta, IL-6 and chemotactic agents IL-8 and LTB4 SEB induced the production of IL-1 beta and IL-8. Epithelial cells exposed for longer periods (48 h) with low concentrations of SEB produced significantly higher levels (P < 0.02) of IL-1 beta and IL-8 (P < 0.05) compared to a 24 h exposure. SEB did not induce the production of IL-6 and LTB4.

T-cell proliferation to superantigen-releasing Staphylococcus aureus by MHC class II-bearing keratinocytes under protection from bacterial cytolysin

Skin colonization with Staphylococcus aureus may exacerbate skin disorders by activation of lesional T cells with release of superantigens. Although T cells are effectively stimulated by staphylococcal superantigens in the presence of epidermal accessory cells, it remains to be elucidated whether in vivo cutaneous colonization with S. aureus can activate T cells. We examined how T cells are stimulated in the presence of keratinocytes by mitomycin C (MMC)-treated S. aureus that are unable to propagate but retain their ability to produce superantigens. Peripheral blood mononuclear cells (PBMCs) proliferated well in response to MMC-treated superantigen-producing S. aureus and bacterial supernatants. When purified T cells were cultured with MMC-treated S. aureus or supernatant in the presence of interferon-gamma-pre-treated keratinocytes, the supernatant, but not MMC-treated S. aureus, stimulated T cells. MMC-treated S. aureus had a cytotoxic effect on keratinocytes. Furthermore, keratinocytes were highly susceptible to alpha-toxin compared with monocytes and B cells functioning as accessory cells in PBMCs. This suggests that a lack of response of T cells to S. aureus plus keratinocytes is due to damage of superantigen-presenting function of keratinocytes by cytolysin. The activity of alpha-toxin was much less stable than that of superantigen during incubation. Given that S. aureus-colonized skin provides circumstances in which viable keratinocytes are exposed to superantigens but not to active cytolysin(s), skin-infiltrating T cells may be effectively stimulated by S. aureus.

Non-Langerhans cell histiocytoses. A new unifying concept

Based on our series of 111 cases of non-Langerhans cell histiocytoses, we present a new unifying concept for this rare group of disorders. The common denominator is the monocyte/ macrophage, which presents with various histologic features probably due to the influence of cytokines. Non-Langerhans cell histiocytoses are classified according to the predominant mononuclear (vacuolated, spindle-shaped, xanthomatized, scalloped, and oncocytic) and/or multinucleate (Touton, ground-glass appearance, Langhans, and foreign body) histiocytic cell types. Variable mixtures of these cell types produce common polymorphous patterns with prominence of vacuolated, spindle-shaped, and xanthomatized histiocytes in juvenile xanthogranulomas and of scalloped and oncocytic histiocytes in adult xanthogranulomas. Rarely, unusual monomorphous reaction patterns are observed: mostly vacuolated histiocytes are seen in the mononuclear variant of xanthogranulomas, (early benign cephalic histiocytosis, and generalized eruptive histiocytoma. Xanthomatized histiocytes predominate papular xanthoma and rarely xanthoma disseminatum, whereas spindle-shaped histiocytes are evident in spindle cell xanthogranuloma and progressive nodular histiocytosis, scalloped histiocytes are evident in most cases of xanthoma disseminatum, and finally oncocytic histiocytes are evident in reticulohistiocytoma and multicentric histiocytosis. Immunohistochemical, ultrastructural, and clinical findings can rationally be adjusted to this unifying concept of non-Langerhans cell histiocytoses. The time course of lesions, the age of the patients, and the presence or absence of underlying internal diseases are, or may, at least partially, be related to and thus explain variations on the theme of the non-Langerhans cell histiocytic reaction.

Staphylococcal toxins and protein A differentially induce cytotoxicity and release of tumor necrosis factor-alpha from human keratinocytes

It has been proposed that toxins and other bacterial protein products of Staphylococcus aureus can act as triggers or persistence factors in several inflammatory skin diseases. In this study, we examined the S. aureus isolates from the skin of patients with atopic dermatitis and psoriasis. We found that the bacterial isolates from these patients exhibited either characteristic superantigenic toxins or thermolabile toxins believed to be staphylococcal alpha-toxin. All of these staphylococcal strains also secreted extracellular staphylococcal protein A. We found significant differences in the action of these toxins on human keratinocytes and keratinocyte cell lines. The superantigenic toxins toxic shock syndrome toxin-1, staphylococcal enterotoxins A and B, and exfoliative toxin-A, as well as staphylococcal protein A, did not induce significant cytotoxic damage in the keratinocyte cell line HaCaT, whereas the staphylococcal alpha-toxin produced profound cytotoxicity. Keratinocyte cytotoxicity induced by staphylococcal alpha-toxin was time and concentration dependent and demonstrated the morphologic and functional characteristics of necrosis, not apoptosis. Addition of alpha-toxin to keratinocytes simultaneously induced cell lysis and tumor necrosis factor-alpha release into the medium within 30 min; apparently, it was constitutive tumor necrosis factor-alpha. On the other hand, superantigenic toxins and, in particular, protein A showed stimulation of tumor necrosis factor-alpha secretion in keratinocytes and release of this cytokine after 6-12 h of incubation. Thus, staphylococcal protein A, alpha-toxin, and superantigenic toxins found in S. aureus isolates from patients with psoriasis and atopic dermatitis can produce direct pro-inflammatory effects on keratinocytes through the release of tumor necrosis factor-alpha. We propose that these effects may be relevant to the induction and persistence of lesions in these two diseases.

The pathogenesis of Staphylococcus aureus in the trauma patient and potential future therapies

BACKGROUND

Staphylococcus aureus is the most frequently isolated pathogen in the trauma patient and uses multiple virulent factors to cause infection. At the cellular level, infection begins with the prokaryotic bacterial cell manipulating the eukaryotic host cell through its virulent factors. Researching this cellular interaction by describing the mechanisms of actions of various virulent factors may lead to new preventive therapies which will make the trauma patient less susceptible to S aureus infections.

METHODS

Surgical, medical, and microbial literature was reviewed to provide an update on S aureus pathogenesis.

RESULTS

Novel future therapies, in addition to antibiotics, are being devised based on understanding the molecular nature of S aureus pathogenesis.

CONCLUSION

The impact of S aureus on trauma will increase as S aureus develops more antibiotic resistance and as the trauma population becomes older and includes an increasing proportion of immunocompromised patients. To meet the challenge of increased virulence, trauma surgeons should be directly involved in the research of microbial pathogenesis.

Inhibitors of sphingolipid synthesis modulate interferon (IFN)-gamma-induced intercellular adhesion molecule (ICAM)-1 and human leukocyte antigen (HLA)-DR expression on cultured normal human keratinocytes: possible involvement of ceramide in biologic action of IFN-gamma

To elucidate the participation of sphingosine and ceramide in the biologic action of cytokines on epidermal keratinocytes, we studied whether inhibitors of sphingolipid synthesis modulate interferon (IFN)-gamma-induced intercellular adhesion molecule (ICAM)-1 and human leukocyte antigen (HLA)-DR expression on cultured normal human keratinocytes. Pretreatment of keratinocytes with L-cycloserine or fumonisin B1, but not 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), significantly suppressed both ICAM-1 and HLA-DR expression induced by IFN-gamma. Because the synthesis of all kinds of sphingolipids is blocked by L-cycloserine and all except that of sphinganine by fumonisin B1, whereas PDMP inhibits the synthesis of glucosylceramide and glycosphingolipids, the result suggests the participation of ceramide and/or sphingosine in IFN-gamma-induced ICAM-1 and HLA-DR expression. Exogenous C2-ceramide reversed the effects of L-cycloserine and fumonisin B1. On the other hand, sphingosine reversed the effect of L-cycloserine, but not of fumonisin B1. These results indicate that ceramide participates in this pathway, as fumonisin B1, but not L-cycloserine, inhibits the synthesis of ceramide from sphingosine. In addition, reverse transcriptase polymerase chain reaction showed that L-cycloserine reduced the mRNA for ICAM-1, HLA-DR alpha, and HLA-DR beta induced by IFN-gamma, and C2-ceramide and sphingosine antagonized the effect of L-cycloserine. Furthermore, the degradation rate of fluorescent sphingomyelin into ceramide in keratinocytes was increased by IFN-gamma, suggesting that IFN-gamma activates sphingomyelin hydrolysis in keratinocytes. These observations suggest the possible role of ceramide in IFN-gamma-induced ICAM-1 and HLA-DR expression on keratinocytes. Ceramide may function as an endogenous modulator mediating the cytokine signals in keratinocytes.

Th2 suppressor cells are more susceptible to sphingosine than Th1 cells in murine contact photosensitivity

Murine contact photosensitivity (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) is a cutaneous delayed-type hypersensitivity reaction in which both positive and negative regulatory pathways exist. The latter pathway is mediated by antigen-specific, CD4+ suppressor T cells (CPS-Ts) that are Th2 cells. We examined the effects of sphingosine and synthetic cell-permeable analogs of ceramide on the cellular kinetics of CPS-Ts and immune lymph node cells from TCSA-photosensitized mice (CPS-LNC), along with other murine T-cell populations. The addition of sphingosine at 10 or 3 microM to in vitro cultures suppressed DNA synthesis of CPS-Ts and Th2 clones, including D10 cells and 24-2 cells, but not that of CPS-LNC or Thl clones, including 23-1-8 and 28-4 cells. This suggested that sphingosine exerts its inhibitory effects preferentially on the proliferation of Th2 cells. Although suppressing DNA synthesis, sphingosine augmented the production and mRNA expression of interleukin-4 (IL-4) and enhanced the expression of the IL-4 receptor in CPS-Ts. In addition, the ability of sphingosine to induce signal transduction of CPS-Ts was confirmed by elevation of the intracellular free Ca++ concentration. Because CPS-Ts exposed to sphingosine exhibited a lower G2M/G1 ratio than control, these seemingly ambivalent phenomena may be caused by retardation of the G1 to S phase progression, a cell-cycle dysregulation known to augment cytokine production. In contrast to sphingosine, cell-permeable ceramide did not affect the proliferation of these cells when stimulated with mitogen/antigen and did not augment IL-4 production by CPS-Ts. Our study suggests that sphingosine modifies the Th1/Th2 balance by preferentially affecting the cellular kinetics of Th2.

Cutaneous exposure to the superantigen staphylococcal enterotoxin B elicits a T-cell-dependent inflammatory response

We analyzed the impact of superantigens secreted by skin-colonizing Staphylococci on the skin and the associated lymphoid tissue following epicutaneous application and intracutaneous injection of small amounts of staphylococcal enterotoxin B (SEB). A single intracutaneous injection of 50 ng of SEB elicited a strong inflammatory response in the skin of BALB/c mice. Three to 6 h later, we observed langerhans cell activation, mast cell degranulation, vasodilation, upregulation of ICAM-1, and induction of VCAM-1 on dermal blood vessels, with vascular adhesion of granulocytes. by 12 to 24 h, cell infiltration of the dermis increased, reaching the epidermis. Among the infiltrating leukocytes, a substantial number of eosinophils was found. After 48 h, the infiltrate was dominated by mononuclear cells. The response to SEB was dose-dependent, and signs of inflammation slowly disappeared over 5 to 7 days. Although the induction of VCAM-1 on dermal blood vessels suggested a role for interleukin-1/tumor necrosis factor-alpha in this reaction, the activation of monocytes/macrophages was not able to substitute for lymphocytes, as severe combined immunodeficiency (SCID) mice (which are lymphocyte-deficient) did not mount an inflammatory skin response to intradermal injection of SEB. The fact that nude mice (T-cell-deficient) also did not mount an inflammatory response to SEB indicated the T-cell dependency of the response. The V beta specificity of the SEB effect was demonstrated by the fact that SJL/J mice, which lack V beta 8+ T cells (the major SEB-reactive T cell population in mice), exhibited much weaker responses. Deletion or tolerization of SEB-reactive V beta T cells was not observed after a single intradermal injection of such minute amounts of SEB.

Hair cycle-dependent changes in skin immune functions: anagen-associated depression of sensitization for contact hypersensitivity in mice

To assess whether hair follicle cycling influences skin immunity, we examined the association between highly synchronized hair follicle cycling and experimental contact hypersensitivity in C57BL/6 mice. Hair cycle synchronization was performed by depilation of hair shafts on the back with telogen skin. Mice were sensitized on the lower back skin with picryl chloride between 0 and 25 d, after anagen induction by depilation, and challenged on the earlobes with picryl chloride 5 d later. The magnitude of contact hypersensitivity was significantly decreased in mice sensitized on day 1, was minimal on day 3 (early anagen), and slowly increased thereafter, reaching level comparable to day 0 on day 25 (telogen). The significantly depressed contact hypersensitivity response in anagen skin was confirmed in mice with spontaneously developed follicles. Lymph node cells taken from mice sensitized with picryl chloride on days 0, 1, and 3 after depilation were cultured in vitro in the presence of syngeneic, haptenized, Langerhans cell-enriched epidermal cells. Marked proliferative responses of lymph node cells to haptenized cells were found in mice not only of day 0, but also of days 1 and 3, suggesting that immune T cells exist even lymph node cells of the low-responsive mice. Flow cytometric analyses demonstrated that the number of intraepidermal Langerhans cells and their functions, including the expression of major histocompatibility complex class II, CD54, and CD86, and mixed epidermal cell lymphocyte reactions, were not changed in skin on days 0,1, and 3. These findings demonstrated that contact hypersensitivity is induced most effectively via skin with telogen hair follicles and that the depressed response in early anagen skin is not simply due to failure in Langerhans cell function or sensitization of T cells.

Superantigens

Superantigens are potent modulators of the immune system. Some of their biological and immunological properties are reviewed here with special attention to their potential significance for cutaneous inflammation, specific skin immune responses and skin diseases.

Keratinocytes-associated chemokines and enzymatically quiescent heparanase induce the binding of resting CD4+ T cells

Whether the chemokines macrophage inflammatory protein-1 beta (MIP-1 beta) and regulated on activation normal T expressed and secreted (RANTES), which interact specifically with glycosaminoglycans and thus mediate the recruitment, attachment, and migration of leukocytes to vascular endothelia and extracellular matrix, are also involved in interactions between CD4+ murine T lymphocytes and keratinocytes was examined. We have previously observed that depending on the local pH, a mammalian extracellular matrix-degrading enzyme, endo-beta-D glucuronidase (heparanase), which cleaves heparin sulfate proteoglycans, can function wither as an enzyme or as an adhesion molecule for CD4+ T lymphocytes. Herein, the involvement of heparanase in T cell-keratinocyte interactions was also probed. At 37 degree C and pH 7.2, radioactively labeled MIP-1 beta, RANTES, and heparanase bound to confluent layers of resting keratinocytes in a saturable and an heparan sulfate- or heparin-dependent manner, and thereby induced the adhesion of resting CD4+ T cells to keratinocytes. At a relatively acidic pH characteristic of inflammatory milieu, enzymatically active heparanase did not bind to the keratinocytes but, rather, inhibited the binding of MIP-1beta, RANTES, and the enzymatically quiescent heparanase to keratinocytes. These results suggest that certain chemokines and heparanase may function to restrict passing leukocytes, notable T lymphocytes, in the cutaneous micro-environment, a site which is continuously challenged with antigens. These keratinocyte-bound lymphocytes can serve as a reservoir of immediate responders to immunological stimuli.

Staphylococcal enterotoxin B upregulates expression of ICAM-1 molecules on IFN-gamma-treated keratinocytes and keratinocyte cell lines

The effects of staphylococcal enterotoxin B (SEB), a Staphylococcus aureus-derived bacterial superantigen, on expression of intercellular adhesion molecule-1 (ICAM-1) were examined in cultured normal and transformed (DJM-1 cells) human keratinocytes by flow cytometry, confocal microscopy, digital image processing, and reverse transcriptase-polymerase chain reaction. SEB significantly upregulated ICAM-1 expression in the interferon-gamma (IFN-gamma)-pretreated, HLA-DR-positive normal keratinocytes and DJM-1 cells in a dose-dependent manner, but not in the untreated, HLA-DR-negative cells. Other toxins such as diphtheria and pertussis toxins did not have the effect. The distribution of SEB and HLA-DR molecules was identical on the IFN-gamma-treated, HLA-DR-positive DJM-1 cells by confocal microscopy. Digital image processing analysis demonstrated that SEB induced a transient increase of intracellular calcium concentration only in the IFN-gamma-treated DJM-1 cells. Pretreatment of the IFN-gamma-treated DJM-1 cells with anti-major histocompatibility complex class II monoclonal antibody completely blocked the effect of SEB. Furthermore, ICAM-1 mRNA was detected in the IFN-gamma-pretreated, SEB-exposed normal keratinocytes by reverse transcriptase-polymerase chain reaction. Our results demonstrate that SEB binds to keratinocytes, presumably via major histocompatibility complex class II molecules such as HLA-DR, triggers calcium mobilization, and induces the synthesis of ICAM-1 molecules. We speculate that, in various cutaneous disorders, SEB penetrates the epidermis and interacts with HLA-DR-positive keratinocytes to upregulate ICAM-1 expression, thus modulating the course of the inflammatory process.

The effects of cyclosporin A and FK506 on proliferation and IL-8 production of cultured human keratinocytes

The present study was conducted to determine whether cyclosporin A (CsA) and FK506 could be effective in inhibiting the proliferation and cytokine secretion of normal human epidermal keratinocytes (NHEK). NHEK proliferation in the presence of CsA and FK506 at the concentrations 10(-9) to 10(-5) M at 24 and 48 h time points was measured colorimetrically by the MTS assay. CsA had inhibitory effects from 10(-6) to 10(-5) M, while FK506 had no effect, except for toxicity at the very highest concentrations (5 x 10(-6) M and higher). NHEK cells spontaneously secrete IL-8 (243.4 +/- 55.5 pg/ml), and this baseline level was augmented by TNF-alpha alone, or synergistically by TNF-alpha and IFN-gamma, which are thought to be secreted by T cells. Neither CsA nor FK506 had any significant effect on either spontaneous or cytokine-stimulated keratinocyte IL-8 production. Therefore, it is most likely that the two drugs indirectly inhibit the keratinocyte inflammatory response through their actions on T cells or other immunocompetent cells.

The role of superantigens in skin disease

Staphylococcus aureus and streptococci secrete a large family of exotoxins involved in the pathogenesis of toxic-shock-like syndromes and have been implicated in several autoimmune disorders. These toxins act as prototypic superantigens capable of binding to major histocompatibility complex proteins on antigen-presenting cells outside the antigen peptide-binding groove and can thereby stimulate cytokine release from macrophages. The superantigen-major histocompatibility complex unit is recognized primarily by the variable region of the T-cell receptor beta chain, and by engaging this region, can activate a large portion of the T-cell repertoire. It is thought that the capacity of these toxins to cause the massive stimulation of T cells and accessory cells such as macrophages, Langerhans cells, and activated keratinocytes accounts for most of their pathologic effects. The current review examines the evidence that implicates a role for these superantigens in the pathogenesis of certain skin diseases.

Cutaneous colonization with staphylococci influences the disease activity of Sézary syndrome: a potential role for bacterial superantigens

It has previously been shown that circulating Sézary cells respond in vitro to superantigenic staphylococcal exotoxins in a manner that is restricted by their V beta usage. This study was conducted to examine whether cutaneous colonization with Staphylococcus aureus influences the activity of the skin lesions of Sézary syndrome, and whether S. aureus isolated from patients with Sézary syndrome stimulates circulating Sézary cells in vitro. Two patients with Sézary syndrome, whose skin was colonized with S. aureus, were treated with antibacterial agents, and the relation between the severity of the skin disease and the degree of S. aureus colonization was assessed. In addition, the patients' peripheral blood mononuclear cells were cultured in the presence of mitomycin C-treated S. aureus or superantigenic staphylococcal toxins. The antibacterial treatment improved the skin disease, and eliminated S. aureus in both patients. In one patient, 98% of the peripheral blood mononuclear cells bore V alpha 2V beta 17 of the T-cell receptor, indicative of the presence of an extremely high percentage of circulating Sézary cells. The peripheral blood lymphocytes from this patient responded well in vitro to superantigenic staphylococcal enterotoxin (SE), but not to SEA or toxic shock syndrome toxin-1, or to mitomycin-treated S. aureus isolated from the same patient. Cutaneous colonization by S. aureus influences the disease activity of CTCL, possibly by activation of Sézary cells by bacterial superantigenic exoproteins.

Cutaneous T-cell lymphoma in association with silicone breast implants

BACKGROUND

Cutaneous T-cell lymphoma (CTCL) is a chronic malignancy of helper T cells with the CD4 phenotype. It occurs less frequently in young women but is increasing in incidence for unknown reasons. Silicone breast implants have been associated with T-cell-mediated autoimmune reactions.

OBJECTIVE

Our purpose was to suggest the hypothesis that CTCL may arise after breast implants and that different patients with CTCL may be stimulated by different antigens.

METHODS

Investigators with many patients with CTCL were queried regarding the occurrence of CTCL in women after breast implants.

RESULTS

Three cases of confirmed CTCL after breast implants were identified and are reported. In one patient with Sézary syndrome and CTCL, the disease went into remission after removal of implants, resolution of chronic staphylococcal infection, and initiation of photopheresis and interferon alfa therapy. Another patient had progressive disease.

CONCLUSION

CTCL may occur in association with breast implants in young female patients, but causality is unknown. If CTCL is antigen driven, then it is likely to result from several different antigens in different groups of patients.

Susceptible responsiveness to bacterial superantigens in peripheral blood mononuclear cells from patients with psoriasis

We investigated the in vitro responses to bacterial superantigens of peripheral blood mononuclear cells taken from patients with psoriasis (one arthropathic, two guttate and four chronic plaque type). We also analysed the relationship between the magnitude of the responses of peripheral blood mononuclear cells to bacterial exotoxins and the number of circulating T cells bearing V beta 2 and V beta 3 regions. The proliferative response of peripheral blood mononuclear cells to Staphylococcal enterotoxin B and toxic shock syndrome toxin-1 was significantly higher in patients with active psoriasis than in normal subjects. An improvement in skin eruption was associated with a decrease in the lymphocyte response to one-half or one-third that of the active phase. There was no significant difference between patients with psoriasis and normal subjects in the percentage of V beta 2- and V beta 3-positive circulating T cells. The percentages of V beta 2-positive and V beta 3-positive cells were not correlated with the levels of responsiveness to toxic shock syndrome toxin-1 and to Staphylococcal enterotoxin B, respectively. These findings suggest that the magnitude of responses of peripheral blood mononuclear cells to bacterial toxins does not depend on the number of T cells reactive with the relevant superantigen, but depends on the extent of skin lesions in psoriasis.

Afloqualone photosensitivity: immunogenicity of afloqualone-photomodified epidermal cells

Afloqualone (AQ) is an oral muscle relaxant and evokes ultraviolet A (UVA)-induced photosensitivity dermatitis as a side effect. Histologic observations of the skin eruption suggest that AQ photosensitivity is mediated not only by phototoxic but also by photoallergic mechanisms. To address the immunological mechanisms of AQ photosensitivity, we examined the immunogenicity of AQ-photomodified epidermal cells in mice. Afloqualone was covalently coupled with bovine serum albumin by irradiation with UVA but not UVB. Because of this ability of AQ to photobind to protein, murine epidermal cells were easily modified with AQ by exposure to UVA. Subcutaneous inoculation of AQ-photomodified epidermal cells successfully induced an antigen-specific delayed-type hypersensitivity in mice. These findings suggest that AQ-photoderivatized epidermal cells are highly immunogenic and that photomodification of epidermal cells with AQ is an initial event to evoke AQ photosensitivity dermatitis.

Accessory cell ability of Langerhans cells for superantigen is resistant to ultraviolet-B light

We examined the effects of ultraviolet-B (UVB) irradiation on the accessory cell ability of Langerhans cells (LC) to induce a T-cell response to a superantigen, staphylococcal enterotoxin B (SEB). The ability of LC-enriched epidermal cells (LC-EC) to evoke a T-cell response to SEB was retained at the doses of UVB (up to 40 mJ/cm2) that profoundly affected the antigen-presenting function of LC-EC for a hapten, trinitrophenyl (TNP), and a protein antigen, conalbumin. Thus, the LC accessory function for superantigens is more resistant to UVB irradiation than that for ordinary antigens. This UVB resistance is presumably due to no requirement of antigen processing for superantigens as chemically fixed or chloroquine-treated LC-EC still retained their ability to induce T-cell responses to SEB. Higher doses of UVB (more than 60 mJ/cm2) reduced the accessory cell ability of LC-EC for SEB up to 50% of control. The addition of monoclonal antibodies against adhesion molecules between LC and T cells to the culture resulted in a substantial suppression of the T-cell response to SEB induced by nonirradiated LC-EC, while the UVB-irradiated LC-EC-induced T-cell response was not significantly blocked with these monoclonal antibodies. This suggested that the reduction of LC ability for superantigen by high doses of UVB is at least partly due to the impairment of adhesion molecules on LC by UVB irradiation.