To 3,3',4',5-tetrachlorosalicylanilide Research Articles

Expression of T-cell cytokines in challenged skin of murine allergic contact photosensitivity: low responsiveness is associated with induction of Th2 cytokines

Murine contact photosensitivity (CPS) to 3,3′,4′,5-tetrachlorosalicylanilide (TCSA) is genetically controlled mainly by the major histocompatibility complex. The H-2 b,d haplotypes are closely associated with high responders, whereas mice with H-2 k are low or non-responders. We found that BALB/c (H-2 d) mice were high responders in CPS not only to TCSA but also to chlorpromazine (CPZ) and benzocaine, whereas AKR/n (H-2 k) mice were hyporesponsive to these three photoallergic agents. To elucidate the relationship between CPS responsiveness and T helper cell induction, the expression of T-cell cytokines was examined by reverse transcriptase polymerase chain reaction in the elicited skin of CPS to the three chemicals. The expression levels of interleukin(IL)-2 and interferon-γ mRNAs were markedly higer in BALB/c mice than AKR/n mice, whereas mRNA for IL-4 was expressed strongly in AKR/n mice. These data suggest that the hyporesponsiveness of CPS to the photoallergens in AKR/n mice is closely associated with the activation/induction of Th2 cytokines at the challenged sites.

Altered Permeability and Disordered Cutaneous Immunoregulatory Function in Mice with Acute Barrier Disruption

In vivo and in vitro T-cell-activating ability of murine epidermal cells (EC) was investigated in acutely barrier-disrupted skin by extraction of epidermal lipids with acetone or removal of corneocytes by tape stripping. Contact sensitivity (CS) to 2,4-dinitrofluorobenzene (DNFB) and picryl chloride (PCl) and contact photosensitivity (CPS) to tetrachlorosalicylanilide (TCSA) were significantly augmented when challenged or sensitized at sites treated with acetone 24 h before, compared with the intact skin. CS to DNFB was also enhanced by tape stripping, but not by water rubbing, suggesting that physical stress or a toxic effect of acetone was not responsible for the augmentation. Semi-quantification of TCSA-EC photoadducts showed markedly increased permeability of hapten in the epidermis 24 h after acetone treatment. Bioactive IL-1alpha was more pronounced in barrier-disrupted than in intact skin. Lymph node T cells from PCl-sensitized mice proliferated significantly more in a hapten-specific and co-stimulatory molecule-dependent manner in response to trinitrophenylated (TNP) EC from acetone-treated skin than to those from untreated skin. Immunofluorescence staining of epidermal sheets and flow cytometric analysis of dispersed EC showed that subpopulations of Langerhans cells (LC) in acetone-rubbed or tape-stripped skin expressed major histocompatibility complex class II CD54 and CD86 molecules at levels higher than the rest of LC and LC from water-treated or untreated epidermis. Therefore, not only increased permeability of hapten through the epidermis but also altered immune functions of EC potentiate T-cell activation in acute barrier disruption. Such augmentation of immune reactivity may be critical to elimination of environmental noxious agents that penetrate easily into the barrier-disrupted epidermis.

Spontaneous Hair Follicle Cycling May Influence the Development of Murine Contact Photosensitivity by Modulating Keratinocyte Cytokine Production

The development of murine contact hypersensitivity is influenced by hair follicle cycling. Here, we have examined hair cycle-associated fluctuations of murine contact photosensitivity (CPS) to tetrachlorosalicylanilide (TCSA) and its immunologic mechanism(s). When the CPS outcome was monitored in correlation with their spontaneous, synchronized hair cycling, mice aged 8 and 14 weeks, with most of their hair follicles in telogen, exhibited strong CPS responses, whereas 4-, 11-, and 16-week-old mice with a predominance of anagen follicles in a large area of their integument exhibited lower responses. This suggests that the development of CPS is inhibited in mice with anagen hair follicles. Antigen-specific, T-cell receptor Vβ7+suppressor T cells, which are recognized to down-regulate the CPS response to TCSA, were not generated in sensitized anagen mice. Culture supernatants of epidermal cells derived from mice with anagen hair follicles contained factor(s) that suppressin vivothe development of CPS. It was found that levels of mRNA for tumor necrosis factor α (TNFα) were markedly decreased in epidermal cells from early anagen to telogen mice, whereas message for IL-1 receptor antagonist (IL-1ra) was transcribed increasingly during this hair cycling. These findings suggest that altered keratinocyte production of these cytokines is involved in mediating the anagen-associated depression of CPS.

The evolution of antidotal therapy in the last decades

Murine contact photosensitivity (CPS) to 3,3′,4′,5-tetrachlorosalicylanilide (TCSA) is genetically controlled mainly by the major histocompatibility complex. The H-2b,d haplotypes are closely associated with high responders, whereas mice with H-2k are low or non-responders. We found that BALB/c (H-2d) mice were high responders in CPS not only to TCSA but also to chlorpromazine (CPZ) and benzocaine, whereas AKR/n (H-2k) mice were hyporesponsive to these three photoallergic agents. To elucidate the relationship between CPS responsiveness and T helper cell induction, the expression of T-cell cytokines was examined by reverse transcriptase polymerase chain reaction in the elicited skin of CPS to the three chemicals. The expression levels of interleukin(IL)-2 and interferon-γ mRNAs were markedly higer in BALB/c mice than AKR/n mice, whereas mRNA for IL-4 was expressed strongly in AKR/n mice. These data suggest that the hyporesponsiveness of CPS to the photoallergens in AKR/n mice is closely associated with the activation/induction of Th2 cytokines at the challenged sites.

Early molecular events induced by tributyltin in murine keratinocytes

Murine contact photosensitivity (CPS) to 3,3′,4′,5-tetrachlorosalicylanilide (TCSA) is genetically controlled mainly by the major histocompatibility complex. The H-2b,d haplotypes are closely associated with high responders, whereas mice with H-2k are low or non-responders. We found that BALB/c (H-2d) mice were high responders in CPS not only to TCSA but also to chlorpromazine (CPZ) and benzocaine, whereas AKR/n (H-2k) mice were hyporesponsive to these three photoallergic agents. To elucidate the relationship between CPS responsiveness and T helper cell induction, the expression of T-cell cytokines was examined by reverse transcriptase polymerase chain reaction in the elicited skin of CPS to the three chemicals. The expression levels of interleukin(IL)-2 and interferon-γ mRNAs were markedly higer in BALB/c mice than AKR/n mice, whereas mRNA for IL-4 was expressed strongly in AKR/n mice. These data suggest that the hyporesponsiveness of CPS to the photoallergens in AKR/n mice is closely associated with the activation/induction of Th2 cytokines at the challenged sites.

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.

Evaluation of ultraviolet-A protection by sunscreen agents using a mouse model of contact photoallergy

This study was conducted to investigate in vivo evaluation of protectiveness by sunscreens in the UVA range using a mouse model of contact photoallergy (CPS) to 3,3′,4′,5-tetrachlorosalicylanilide (TCSA). Mice were sensitized with TCSA painting plus UVA irradiation (TCSA/UVA) on the abdomen and, 5 days later, challenged with TCSA/UVA on the earlobe. Each of four sunscreen agents, benzophenone-3, Parsol 1789, p-aminobenzoic acid, and 2-ethyl-hexyl- p-methoxycinnamate, was applied to the earlobes before irradiation. Their protective efficacy was evaluated in the degree of inhibition of both ear swelling responses and TCSA-epidermal cell photoadduct formation. Two UVA-absorbing sunscreens, benzophenone-3 and Parsol 1789, dramatically inhibited the ear swelling response, while the two UVB-absorbers exhibited a much less suppressive effect. The UVA-absorbing agents functioned via inhibiting the formation of TCSA-epidermal cell photoadducts. This method is thought to be useful for in vivo estimation of UVA protection provided by sunscreens against the exquisite sensitivity involved in photoallergy.

Inhibitory Effect of Melanin Pigment on Sensitization and Elicitation of Murine Contact Photosensitivity: Mechanism of Low Responsiveness in C57BL/10 Background Mice

We have shown that murine contact photosensitivity (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) is genetically controlled mainly by the major histocompatibility complex. The H-2b,d haplotypes are closely associated with high responders, whereas mice with the H-2k are non-responders. Irrespective of their H-2 haplotypes, the C57BL/10 (B10) background strains, including B10, B10.D2, B10.A, and B10.BR, possessing black fur color, were low or nonresponders in CPS to TCSA. In B10 mice, however, high-sensitivity responses were induced when subcutaneous inoculation of epidermal cells (ECs) photomodified in vitro with TCSA was used for both immunization and challenge, suggesting that the epicutaneous route for induction and elicitation is defective in B10 background mice. F1 mice obtained by crossing high-responder BALB/c and low-responder B10 mice, possessing agouti fur color, were non-responders of CPS. The magnitude of CPS in the F2 mice derived from F1 (BALB/c X B10) siblings varied from low to high. When these F2 mice were divided into five groups with regard to fur color, the magnitude of reaction was correlated with the fur color and there was inverse relationship between the magnitude of CPS and the amount of melanin pigment in earlobe ECs. Furthermore, the in vivo formation of TCSA-EC photoadducts was negatively correlated to the melanin amount in earlobes. These observations suggested that the failure in CPS of the B10 background mice stems from inability of in vivo photocoupling of TCSA to ECs, presumably due to absorption of ultraviolet radiation by melanin pigment.

Examination of Tetrachlorosalicylanilide (TCSA) Photoallergy Using In Vitro Photohapten-Modified Langerhans Cell-Enriched Epidermal Cells

Lymphocytes from BALB/c mice photosensitized in vivo to tetrachlorosalicylanilide (TCSA) were investigated to determine whether they could be stimulated to proliferate when cultured with Langerhans cell-enriched cultured epidermal cells (LC-EC) photohapten-modified in vitro with TCSA + UVA radiation. Cultured LC-EC were photohapten-modified in vitro by irradiation in TCSA-containing medium using a 1000-watt solar simulator equipped with filters to deliver primarily UVA radiation (320-400 nm). Lymphocytes from TCSA-photosensitized mice were incubated with LC-EC that had been treated in vitro with 0.1 mM TCSA and 2 J/cm2 UVA radiation (TCSA + UVA). Responder lymphocytes demonstrated a significant increase in their blastogenesis response compared to lymphocytes that were incubated with LC-EC irradiated with UVA prior to treatment with TCSA (UVA/TCSA) or with LC-EC that had received no treatment. Lymphocytes from naive mice or mice photosensitized with musk ambrette (MA) demonstrated a significantly lower response to LC-EC modified with TCSA + UVA, indicating the specificity of the response. Maximum blastogenesis response was achieved when LC-EC were treated with 0.1 mM TCSA and a UVA radiation dose of at least 0.5 J/cm2. Epidermal cells depleted of LC by treatment with anti-Ia antibody plus complement or by an adherence procedure were unable to stimulate this blastogenesis response. Epidermal cells treated in vitro with TCSA + UVA demonstrated enhanced fluorescence compared to control cells. The fluorescence observed was not restricted to any specific epidermal cell type; however, fluorescence microscopy studies revealed that dendritic Ia-positive cells, presumably LC, were also TCSA fluorescent. Flow cytometry showed that Ia-positive epidermal cells demonstrated the greatest UV fluorescence when treated with TCSA + UVA compared to both cells irradiated with UVA and subsequently treated with TCSA and untreated cells. This is consistent with the enhanced antigen presentation capability of TCSA + UVA treated LC-EC, which leads to the conclusion that LC photohapten-modified in vitro with TCSA + UVA demonstrate enhanced TCSA fluorescence and are capable of stimulating lymphocytes from TCSA photosensitized mice in an antigen-specific manner.

Genetic control of contact photosensitivity to tetrachlorosalicylanilide: II. Igh complex controls the sensitivity induced by photohapten-modified spleen cells but not epidermal cells

We studied the genetic control of murine contact photosensitivity (CPS) 1 1 Abbreviations used: Ag, antigen; C, complement; CPS, contact photosensitivity; CS, contact sensitivity; CY, cyclophosphamide; DTH, delayed-type hypersensitivity; EC, epidermal cell; ec, epicutaneous; Ig, immunoglobulin; Igh, Ig heavy chain gene complex; Igh-V, variable region of Igh; Igh-C, constant region of Igh; LC, Langerhans cell; Mφ, macrophage; PBS, phosphate-buffered saline; PCI, picryl chloride; photoTCSA-, TCSA-photomodified; SC, spleen cell; sc, subcutaneous; TCSA,3,3′,4′,5-tetrachlorosalicylanilide; TNBS, 2,4,6-trinitrobenzene sulfonic acid; TMA, phenyltrimethylamino; TNP, trinitrophenyl; Ts, suppressor T cells. to 3,3′,4′,5-tetrachlorosalicylanilide (TCSA) that was induced by subcutaneous injection of TCSA-photomodified epidermal cells (photoTCSA-EC) and spleen cells (photoTCSA-SC). With regard to the H-2 locus, sensitization with both types of photohaptenated cells showed the same pattern of CPS responses; H-2 k and H-2 b,d haplotypes were closely associated with low and high responders, respectively. On the other hand, the Igh locus affected the CPS reaction induced by photoTCSA-SC but not-EC; the Igh-1 d allotype was related to low responsiveness, while high responders possessed Igh-1 a,b. Thus, the photoTCSA-SC sensitization was controlled by H-2 and Igh in a codominant manner. The photoTCSA-SC-induced responses of H-2 k but not Igh-1 d mice were enhanced by CY pretreatment, suggesting that the mechanisms of low responsiveness in H-2 k and Igh-l d mice were different. H-2 identity between donors of photoTCSA-EC and recipients was sufficient for effective sensitization, whereas both H-2 and Igh between donors of photoTCSA-SC and recipients should be identical to obtain maximum sensitization. This further confirmed the involvement of the Igh complex in the genetic control of CPS evoked by photoTCSA-SC. B cells as well as macrophages served as an effective presentation template for the photoTCSA-SC sensitization in the high responder Igh-1 a mice, whereas B cells failed in inducing the CPS reaction in the low responder Igh-1 d mice. These results suggest that B cells play an essential role in the Igh control phenomenon seen in the photoTCSA-SC sensitization. The present study demonstrated that CPS induced by photohapten-modified cells are differentially regulated by the H-2 and Igh gene loci depending on the cell type used for sensitization.

Ultraviolet-induced suppressor T cells and factor(s) in murine contact photosensitivity: III. Mode of action of T-cell-suppressor factor(s) and interaction with cytokines

The mode of action of T-cell-suppressor factor (TsF) induced by ultraviolet B (UVB) preirradiation in terms of interaction with several cytokines was studied. Suppression of murine contact photosensitivity (CPS) to 3,3′,4′,5-tetrachlorosalicylanilide (TCSA) by preirradiation of the sensitizing site to low doses of UVB was caused by antigen-specific suppressor T cells (Ts) and was not associated with the generation of efferent limb-acting suppressor cells. TsF released by Ts inhibited the proliferation of immune lymph node (LN) cells in vitro and reduced interleukin (IL)-2 production of these cells in an antigen-specific fashion without affecting the IL-2 receptor (IL-2R) expression. Both rIL-2 and rGM-CSF have the ability to restore CPS responses in the UVB-preirradiated mice when administered after but not before photosensitization. However, rIL-2 but not rGM-CSF counteracted the in vivo inhibitory effect of TsF. rGM-CSF did not affect the density of I-A + epidermal Langerhans cells (LCs). It was suggested that TsF inhibited IL-2-mediated immune T-cell proliferation, while rGM-CSF reconstituted the CPS by enhancing the function of photodamaged LCs. These results indicate multiple steps of the UVB-induced immunosuppression circuit, each of which seems to be controlled by different immunomodulators.

Genetic Control of Contact Photosensitivity to Tetrachlorosalicylanilide. I. Preferential Activation of Suppressor T Cells in Low Responder H-2k Mice

The genetic control of contact photosensitivity (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) was studied in H-2- and IgH-congenic mice. The H-2 complex was found to play a major role in determining the pattern of responsiveness, whereas the effect of the Igh locus on the response was not apparent. The H-2k haplotype was closely associated with low responders, whereas mice with the H-2b,d alleles were high responders. The responsiveness of the H-2k strains was converted from low to high levels by treatment with cyclophosphamide (CY) before photosensitization. Transfer of spleen cells from photosensitized H-2k mice showed a suppressive effect on the development of the CPS reaction of syngeneic recipients pretreated with CY. These spleen cells contained antigen-specific CD4+, CD8- suppressor T cells (Ts) that functioned in the induction phase of CPS. The in vitro proliferation of immune lymph node T cells pulsed with photohapten-coupled cells plus peritoneal adherent cells was suppressed by the addition of anti-I-A monoclonal antibody in both H-2d and H-2k strains, suggesting that the I-A molecule are responsible for inducing the positive immune response. On the other hand, such proliferation was significantly enhanced by the addition of anti-I-E alpha antibody in H-2k, but not H-2d, mice. This implies that the low responsiveness of CPS in the H-2k strain is due to the preferential activation of Ts via I-Ek molecules. The present observation further supports the important role of the I-E molecule in the suppressor circuit of CPS to TCSA.

An optimized lymphocyte blastogenesis assay for detecting the response of contact sensitized or photosensitized lymphocytes to hapten or photohapten modified antigen presenting cells

In vitro assays for predictive identification of contact sensitizers of photosensitizers are more quantifiable than current skin test methods and have the potential to reduce animal use. Mice were sensitized to various strong contact allergens, then an optimized lymphocyte blastogenesis assay was used for detecting the proliferation of lymph node lymphocytes from those mice in response to soluble antigen or hapten-modified antigen presenting cells in culture. In vivo sensitization to oxazolone (OXAZ), a prototype sensitizer, resulted in poor in vitro lymphocyte blastogenesis to a solubilized OXAZ preparation. To increase the assay sensitivity, dendritic cells from the draining lymph nodes of OXAZ-painted mice or OXAZ-modified Langerhans cell-enriched cultured epidermal cells (EC) were used as antigen presenting cells. This increased the OXAZ-specific response greater than 10-fold and 50-fold, respectively. This approach has since been used to demonstrate significant, albeit smaller, responses to weaker contact allergens such as nickel sulphate. EC were also used as antigen-presenting cells for in vitro lymphocyte blastogenesis assays designed to detect photoallergens. Lymphocytes from mice photosensitized to tetrachlorosalicylanilide (TCSA) showed a significantly increased response to EC previously photohapten-modified by treatment with TCSA plus ultraviolet A (UVA), as compared with lymphocytes cultured with EC treated with TCSA but no UVA. The lymphocyte blastogenesis assay may have potential as a predictive screen to identify contact and photocontact allergens.

Optimization of tetrachlorosalicylanilide and ultraviolet A doses at sensitization and challenge for contact photosensitivity in the mouse.

We studied contact photosensitivity (CPS) to tetrachlorosalicylanilide (TCSA) in BALB/cJ mice with various doses of TCSA and UVA at sensitization and challenge. From these studies we recommend the following protocol: sensitization on days 0 and 1 with 50 microliters of 1% TCSA followed by 3 J/cm2 of UVA, and challenge on day 7 with 10 microliters of 3% TCSA followed by 6 J/cm2 of UVA. This gave an ear swelling response of 27.4 +/- 0.6 x 10(-3) (mean +/- standard error). We also demonstrated that there is reciprocity between volume and concentration of TCSA at sensitization but not between TCSA and UVA doses at sensitization.

Mechanisms of Contact Photosensitivity in Mice. VI. Oxygen Intermediates Are Involved in Contact Photosensitization but Not in Ordinary Contact Sensitization

To investigate the possible participation of oxygen intermediates (OIs) in the contact photosensitization process, mice were treated with long-acting liposomal-superoxide dismutase (L-SOD) before photosensitization. Photosensitization to 3,3',4',5-tetrachlorosalicylanilide (TCSA) was significantly suppressed by the pretreatment of mice with L-SOD. This suppression was not mediated by suppressor cells or due to an unresponsive state produced by the use of L-SOD. Rather, the suppression appeared to be due to the failure of production of photoallergen. L-SOD treatment induced the suppression of contact photosensitivity to TCSA but not ordinary contact sensitivity to TCSA or dinitrofluorobenzene, suggesting that the production of photoallergen is more critically dependent on the presence of OIs than that of ordinary contact allergen. The results provide evidence that OIs are produced by light absorption in the presence of oxygen and react with the biologic substrate to form photoallergens.

The role of suppressor cells in the induction of murine photoallergic contact dermatitis and in its suppression by prior UVB irradiation.

Induction in mice of marked photoallergic contact dermatitis (PCD) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) with UVA (320 to 400 nm) radiation requires pretreatment with cyclophosphamide (CY). Attempts to induce photoallergic contact dermatitis without CY result in only a small degree of sensitivity, accompanied by significant net splenic suppressor cell activity. These suppressor cells are antigen specific, inhibit the induction but not the elicitation of photoallergic contact dermatitis to TCSA, and are T lymphocytes. Exposure of mice to UVB (280 to 320 nm) radiation at a site distant from that of sensitization, before CY administration and sensitization, inhibits the development of photoallergic contact dermatitis. This is analogous to the suppression of allergic contact dermatitis (ACD) observed in mice after exposure to UVB radiation; such suppression is accompanied by the formation of antigen-specific splenic suppressor cells. However, in contrast to the findings with allergic contact dermatitis, splenic suppressor cells are not detected in mice that are treated with UVB radiation before CY administration and sensitization to TCSA. This is presumably because CY prevents their formation. This provides evidence that UVB-irradiated mice have a second form of anergy that is not mediated by suppressor cells.

Mechanisms of Contact Photosensitivity in Mice: II: Langerhans Cells Are Required for Successful Induction of Contact Photosensitivity to TSCA

The role of Langerhans cells in the induction of contact photosensitivity (CPS) to tetrachlorosalicylanilide (TCSA) was investigated in mice. CPS was induced by 2 daily paintings of 50 microliters of 1% TCSA in acetone plus black light irradiations for 2.5 hr. Both ears were challenged with 20 microliters of 0.1% TCSA in ethanol plus black light irradiation for 2.5 hr on day 5, and ear thickness was read at 24 hr. The density of LCs detected as ATPase-positive cells dramatically decreased 2 days after exposure to UVB. CPS was not induced by painting the photoallergen to the skin which had been pre-irradiated with UVB. The ear swelling response returned to the normal level when the mice were sensitized 12 days after UVB exposure in accordance with the complete regeneration of ATPase-positive cells. Dose of UVB in the present study did not affect the development of CPS through systemic mechanism. These demonstrations indicate that LCs play an important role in the induction of CPS.

Three zone rocket immunoelectrophoresis for the quantification of C 3d: Circulating levels of C 3d during human pregnancy

The genetic control of contact photosensitivity (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) was studied in H-2- and IgH-congenic mice. The H-2 complex was found to play a major role in determining the pattern of responsiveness, whereas the effect of the Igh locus on the response was not apparent. The H-2k haplotype was closely associated with low responders, whereas mice with the H-2b,d alleles were high responders. The responsiveness of the H-2k strains was converted from low to high levels by treatment with cyclophosphamide (CY) before photosensitization. Transfer of spleen cells from photosensitized H-2k mice showed a suppressive effect on the development of the CPS reaction of syngeneic recipients pretreated with CY. These spleen cells contained antigen-specific CD4+ CD8− suppressor T cells (Ts) that functioned in the induction phase of CPS. The in vitro proliferation of immune lymph node T cells pulsed with photohapten-coupled cells plus peritoneal adherent cells was suppressed by the addition of anti-I-A monoclonal antibody in both H-2d and H-2k strains, suggesting that the I-A molecule are responsible for inducing the positive immune response. On the other hand, such proliferation was significantly enhanced by the addition of anti-I-Eα antibody in H-2k, but not H-2d, mice. This implies that the low responsiveness of CPS in the H-2k strain is due to the preferential activation of Ts via I-Ek molecules. The present observation further supports the important role of the I-E molecule in the suppressor circuit of CPS to TCSA.

Photomaximization test for identifying photoallergic contact sensitizers.

The photomaximization procedure was designed to identify topical photocontact sensitizers following the format of the maximization test for contact sensitizers. The test agent is applied for 24 hours followed by exposure to three Minimal Erythema Doses (MED) of solar simulated radiation twice weekly for 3 weeks (six exposures) in a panel of 25 white Caucasoids. The subjects are challenged 2 weeks later with 4.0 J/cm2 of long-wave ultraviolet radiation (UV-A). Photocontact sensitization was induced to 3,3'4',5-tetrachlorosalicylanilide (TCSA); dibromosalicylanilide (DBS) but not to tribomosalicylanilide unless the latter was contaminated with DBS. Jadit and bithionol were weak photoallergens. The highest rate of sensitization was given by 6-methylcoumarin, a widely used synthetic fragrance. Hexachlorophene and trichlorocarbanilide were negative.

Photocontact allergic reactions. Elicitation by low doses of long ultraviolet rays.

Subjects experimentally photocontact sensitized to tetrachlorosalicylanilide (TCSA), tribromosalicylanilide (TBS), and bithionol were studied with regard to the quantity of long ultraviolet rays (UV) necessary to elicit reactions. Less than one second of high energy long UV, about 20 seconds or less of midday summer sunlight, will elicit photoallergic reactions in highly sensitized persons. Unlike sunburn, photoallergic reactions can readily occur on the hairy scalp and palms, though usually of lesser intensity. Reactions can be elicited through cotton and woolen cloth, adhesive tape, and bond paper. Two thicknesses of desk blotter paper afford a complete light seal.