Mechanism of densensitization in DNCB-contact sensitive guinea pigs

Oral hyposensitization in patients with contact dermatitis from Parthenium hysterophorus

Parthenium hysterophorus is the commonest cause of airborne contact dermatitis in northern India. Treatment is mostly palliative and consists of repeated courses of antihistamines and topical and/or systemic corticosteroids. We have evaluated the effect of oral hyposensitization as an alternative therapeutic modality. In 70% of those patients who completed the study, there was a gradual improvement in their clinical status, as evident from a fall in their clinical severity score for eczema. 30% of patients had an exacerbation during the course of the study and hence hyposensitization in them was stopped. Patients tolerated therapy well and no significant side-effects were seen, except for abdominal pain, 'heartburn' and cheilitis.

Effects of immunological responsiveness on Langerhans cell behavior in contact sensitization

The epicutaneous application of haptens results in a functional activation of the antigen-presenting Langerhans cells (LCs) which is necessary for the induction of contact sensitivity. In this ultrastructural study, we investigated the effects of the immune response on these cellular properties of the LCs by using 2 strains of guinea pigs with genetically determined high and non responsiveness, respectively, to the strong sensitizer 2,4-dinitrochlorobenzene (DNCB). After skin painting, both strains showed a similar cellular and endocytotic activation of the LCs and a similar intraepidermal localization of DNCB on immunoelectron microscopical visualization. There were however few LC-lymphoid cell interactions in the non responders, in contrast to numerous such appositions in the other strain. Intravenous tolerization with 2,4-dinitrobenzene-1-sulfonic acid, which is known to block the DNCB receptor of T cells, hampered the lymphoid cell interactions in the DNCB treated high responders, but it did not affect the LC activation. These in vivo observations demonstrate that the hapten-induced changes of the LC properties is the initial, T-cell independent event in contact sensitization.

Non-sensitizing epicutaneous skin tests prevent subsequent induction of immune tolerance

Oral administration of nickel or chromium to naive guinea pigs results in immune unresponsiveness to subsequent induction of allergic contact hypersensitivity. Such "oral tolerance" depends on the oral dose, is antigen specific, T-suppressor-cell mediated, and very persistent. In contrast, oral antigen administration to sensitized animals results at best in transient desensitization. Here we report that even non-sensitizing epicutaneous skin contacts prevented the subsequent induction of oral tolerance. These data support the view that primed T cells are less sensitive to suppressor T-cell function than naive T cells.

Piroxicam has at least two epitopes for contact photoallergy

We have demonstrated previously in guinea pigs that the induction of photocontact sensitivity to piroxicam (PXM) also induces a state of cross-reactive contact hypersensitivity to two compounds having structurally related elements, thimerosal (TMS) and thiosalicylate (TOS). The present study was conducted to determine whether oral administration of TOS would desensitize guinea pigs previously photosensitized with PXM. At the same time, the spectrum of reactivities against these compounds and against tenoxicam (TXM) which resembles only piroxicam was assessed by appropriate sensitizing and eliciting protocols. As expected, animals photosensitized to PXM developed reactivities against all four compounds, PXM and TXM (photosensitivity) and TMS and TOS (contact sensitivity). By contrast, photosensitization with TXM induced cross-reactivity only against PXM. Moreover, the induction of contact sensitivity against TMS or TOS induced photosensitive cross-reactivity to PXM, but not to TXM. Finally, the oral administration of TOS produced a transient desensitization only for TMS and TOS. These results suggest that photosensitization with PXM induces two distinct reactivities. The first reactivity cross-reacts with TMS and TOS and is suppressible with orally administered TOS. The second cross-reacts only with TXM and is not suppressible with oral TOS. We conclude that PXM acquires at least two distinct immunogenic epitopes when exposed to UVA irradiation.

Hyposensitization to urushiol among Japanese lacquer craftsmen: results of patch tests on students learning the art of lacquerware

8 subjects learning the art of lacquerware were patch tested to urushiol before and after contact with lacquer, in order to document whether hyposensitization to urushiol occurred among Japanese lacquer craftsmen. Simultaneously, we performed patch tests on 2 urushiol-sensitized controls who had no contact with lacquer during the investigation. Lacquer is made from the sap of the Japanese lacquer tree and raw lacquer is composed of 60-65% urushiol and its oligomer. 5 of the 8 subjects showed positive reactions to urushiol 1 month after their first contact. They became negative or less positive after prolonged (9 or 10 months) exposure to lacquer. As reactions to urushiol decreased, dermatitis became less severe. Controls showed consistently high reactions. However, 1 subject showed persistently strong reactions to urushiol. Unlike the other 7 subjects, he was previously sensitized to urushiol before the first contact with lacquer. The remaining 2 subjects showed no reaction throughout our investigation. These results strongly suggest that hyposensitization to urushiol does occur among Japanese lacquer craftsmen.

Local and systemic desensitization induced by repeated epicutaneous hapten application

Frequent skin exposure of guinea pigs to the contact sensitizing agents dinitrochlorobenzene or 4-ethoxymethylene-2-phenyloxazolone induced both systemic hyposensitization and local unresponsiveness within 8 weeks. Both phenomena were hapten-specific. Decreased systemic reactivity in repeatedly painted guinea pigs is probably not due to receptor blockade or the development of hapten-specific antibodies, but rather to transient sequestration of hapten-specific effector cells within lymph nodes draining the site of hapten exposure. After discontinuation of allergen exposure, effector cells return into the circulation, as indicated by a reversal of systemic hyporesponsiveness within 5 weeks. The persistence of a cellular infiltrate at the site of repeated application and the hapten-specific unresponsiveness at this site suggest that suppressor cells play a role in local unresponsiveness. Upon discontinuation of allergen exposure, local unresponsiveness rapidly dissolves (within one week). Since the circulation is still depleted of effector cells, residual hyporesponsiveness may persist for longer periods.

Desensitization of contact allergy to DNFB in mice. III. Characteristics of immediate desensitization induced by haptenated spleen cells

The immediate effects and mechanisms of desensitization of contact sensitivity to dinitrofluorobenzene (DNFB) were investigated. Intravenous injection of dinitrophenol (DNP)-labeled syngeneic spleen cells caused significant antigen-specific inhibition (greater than 40%) of the contact response within 24 hr in mice that had been sensitized 2 weeks prior to desensitization. With low concentrations of the hapten used for labeling, allogeneic spleen cells were found to be more efficient than syngeneic ones in inducing the down-regulation of the contact response. The most efficient desensitization was produced by DNP-cells that differed from the recipient at the MLS locus. Haptenated spleen cells induced the production of suppressor mechanisms, as spleen cells from animals desensitized with DNP-cells were able to down-regulate recipients in adoptive transfer and could block the passive transfer of contact sensitivity. Procedures that interfere with the development of suppressor cells, e.g., cyclophosphamide and adult thymectomy, interfered with desensitization by DNP-cells. These results are in contrast to desensitization with soluble dinitrobenzenesulfonic acid (DNBS), where suppressor mechanisms have not been shown. The mechanisms for desensitization depend upon the form of the desensitizing antigen.

Labeled bleomycin as a tumor localizing agent III. Selectivity of tumor tissue uptake of the different forms of [57Co] bleomycin A2 and B2

The cell uptake of the different forms (I and II) of [57Co]bleomycin A2 and B2 was studied in a Rhabdomyosarcoma cell culture. The results show that the uptake of form I appears to be significantly higher than the uptake of form II. The evidence presented indicates that form I is formed in vivo as well as in vitro from form II by biotransformation. Transferrin stimulates the uptake of Co-bleomycin B2 form I only. As a result of trypsin treatment, it is suggested that form II binds only on the outer cell membrane and is not able to pass this membrane.