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Lymph nodes--and to a lesser extent spleen cells--from guinea-pigs tolerant to DNCB contact sensitivity, when injected into normal syngeneic guinea-pigs, decrease the ability of the recipients to become sensitized to contact with DNCB. The difference between the complete tolerance transferred by parabiosis with tolerant partners and the partial tolerance induced by transfer of tolerant cells can be explained by the different numbers of cells homing in the recipients. The tolergen does not play any role in the transfer of tolerance.

in the present paper it is shown that both induction and elicitation of 2,4-dinitrochlorobenzene-contact sensitivity in guinea pigs are genetically controlled. This genetic control is operating by two somehow different mechanisms. The recognition of hapten on allogeneic macrophages during the inductive phase is suppressed by the allogeneic response against these macrophages whereas the elicitation upon transfer of syngeneically primed lymphocytes is limited by the identity of at least some components of the major histocompatibility complex. This nonidentity contradicts the rule of carrier specificity, which is a requirement for all delayed type hypersensitivity reactions. Furthermore, the presentation of haptens to primed cells is less restricted than presentation of protein antigens.

The different immunologic activities of lymph node and spleen cells as compared to peritoneal exudate cells were studied in temporarily desensitized, DNCB-contact-sensitive guinea pigs. Lymph node (and spleen) lymphocytes: (a) transfer contact sensitivity to syngeneic recipients when harvested at the time of unresponsiveness; (b) are only temporarily inactivated in tolerant recipients by the desensitizing procedure; (c) enter the lymph node (or spleen) compartments in a higher proportion than peritoneal exudate cells; (d) are not susceptible to inactivation in vitro; and (e) are not permanently desensitized when released into the circulation by an intravenous injection of Bordetella pertussis vaccine. These results indicate that the resistance of primed lymph node cells to the desensitizing procedure may account for the reappearance of contact sensitivity in desensitized guinea pigs.

The effect of suppressor cells on the formation of effector cells was studied by comparing the development of DNCB contact sensitivity in cyclophosphamide-treated (suppressor cells eliminated) and non-treated (suppressor cells present) guinea-pigs. From experiments in four different models of generation of effector cells the following conclusions are drawn: (1) impulses activating the formation of effector cells also activate suppressor cells; (2) under conditions of conventional immunization, suppressor cells are activated later than effector cells; (3) elimination of suppressor cells results in an increase in the intensity and duration of specific skin reactions.

In vitro stimulation of lymphocytes from DNCB contact-sensitive guinea pigs is achieved by several DNP conjugates. Optimal results are obtained by DNP-modified macrophages. The degree of in vitro lymphocyte activity, demonstrated by DNA synthesis, depends on the cell origin, the interval between sensitization and harvest of lymphocytes and the immunological status of the animals.

Specific unresponsiveness to DNCB contact sensitivity has been induced in guinea pigs by a combined application of two immunosuppressive agents, cyclophosphamide and antithymocyte serum, to guinea pigs during the period of sensitization with DNCB. This tolerance was specific since the reactivity to an unrelated hapten (oxazolon) was not impaired by the previous immunosuppressive treatment. The unresponsiveness induced by immunosuppressive treatment has not been reversed by an additional treatment with the high dose of cyclophosphamide known to reverse hapten-induced tolerance, and has not been transferred by parabiosis from tolerant to normal partners. From these results it is concluded that specific unresponsiveness induced by immunosuppressive agents is not mediated by suppressor cells but is rather based on clonal deletion. The relative in unstability of this tolerance may be due to formation of new antigen-reactive cells from undeleted precursors.

Lymph node lymphocytes from guinea pigs sensitized with the hapten homogenized in Freund's complete adjuvant or pretreated with cyclophosphamide shortly before an epicutaneous sensitization are capable of responding in vitro to a larger set of antigenic preparations than the lymphocytes from only epicutaneously sensitized animals. This may be due to a formation of a larger set of antigenic determinants when the hapten was homogenized in Freund's complete adjuvant or to a formation of a larger repertoire of lymphocytes capable of recognizing these determinants as it might be the result of pretreatment with cyclophosphamide. These procedures may also change the proportion of responding cells in the lymphocyte suspensions.

Dinitrophenylated macrophages are efficient inducers of contact sensitivity and of tolerance to dinitrochlorobenzene, depending on the mode of application. Contact sensitivity induced by an intradermal injection of DNP-M phi is genetically restricted, whereas tolerance induced by an intravenous injection is, in guinea pigs, not under control. This tolerance is complete in the majority of animals, but is reversed by DNCB in Freund's complete adjuvant and prevented by pretreatment with cyclophosphamide. Tolerance induced by an intravenous injection of the unconjugated hapten is not reversed by DNCB in FCA, but is abrogated by an intradermal injection of DNP-M phi. This abrogation does not occur, however, when DNCB in FCA is applied simultaneously with the DNP-M phi. In further experiments, it is demonstrated that the genetic restriction of induction of contact sensitivity by DNP-M phi is on the level of antigen recognition and is not due to the nonidentity of the Ia structures on macrohages used for induction and the Ia structures involved in elicitation of contact sensitivity.

1. Female guinea pigs made tolerant before pregnancy do not transfer tolerance to their offspring. This result favours the concept of cellular mechanism of tolerance. 2. Guinea pig fetuses become tolerant when exposed to the tolerogen in the last two weeks of pregnancy. This is due to active tolerization by the tolerogen passing the placental barrier. 3. Fetuses exposed to the antigen earlier did not develop tolerance. This is due to immunological immaturity rather than to insufficiently developed vascularization. No functional active depot of tolerogen is formed. 4. Guinea pigs become immunologically mature between the 54th and 61st day of fetal live.

Contact sensitivity to dinitrochlorobenzene (DNCB) in guinea pigs could be rapidly suppressed by intravenous injection of dinitrobenzene sulfonic acid sodium salt (DNBSO3). This suppression is transient and antigen-specific. Macrophages from desensitized animals are not inactivated as shown by their ability to react, both in vivo and in vitro to lymphokines produced in a separate system. Therefore, effector lymphocytes are considered the target for the desensitizing antigen. Using an adoptive transfer system it was demonstrated that effector lymphocytes are inactivated by a direct effect of the hapten. Since this inactivation can be reversed by trypsin treatment, a receptor blockade of effector lymphocytes is proposed as the mechanism of desensitization of DNCB-contact sensitive guinea pigs. This does not exclude the possibility that additional mechanisms such as suppressor cells, compartmentalization or endogenous proliferation of lymph node lymphocytes may play an additional role.

Cyclophosphamide (CY) treatment known to enhance the normal cell-mediated immune response by selectively inhibiting the function of suppressor cells abrogates tolerance by pretreatment when tolerant animals are sensitized 3 days after the intraperitoneal injection of CY. The tolerance during the primary response is also reversed by CY treatment, indicating that in both these types of unresponsiveness suppressor cells may be operating. However, CY treatment did not influence the short-lasting unresponsiveness induced in already sensitized guinea-pigs by the intravenous injection of tolerogen. These findings corroborate the idea that the mechanism of desensitization is different from that of tolerance induced by pretreatment of during the primary response.

The article reviews the recent experimental data that influenced the present concept, of contact sensitivity. Particular emphasis is on the mechanism of stimulation of antigen-inexperienced specific lymphocytes, the eliciting phase, and the role of suppressor cells in sensitization and tolerance. [ABSTRACT FROM AUTHOR]

Contact sensitivity and production of anti-DNP-antibodies induced by epicutaneously applied dinitrochlorobenzene (DNCB) can be permanently suppressed by a previous intravenous injection of a high dose of dinitrobenzene- sulphonate (DNBSO3). The animals fail to develop a paracortical area rich in pyroninophilic cells, in lymph nodes regional to the local application of hapten, characteristic of sensitized controls. Following the injection of lymphoid cells from normal syngeneic donors into these unresponsive animals, large pyroninophilic cells develop in the paracortical area 4 days after sensitization and in some cases antibody production is restored. However, contact sensitivity remains suppressed. If a high dose of DNBSO3 (600 mg/kg) is injected intravenously on the same day as DNCB is applied locally, or when a low dose of DNBSO3 (60 mg/kg) is administered 12 weeks before DNCB, contact sensitivity and production of anti- DNP-antibodies are also suppressed but in such animals the development of a paracortical area containing large pyroninophilic cells is not inhibited. In both cases an immune reaction can be suppressed in the presence of a paracortical area containing large pyroninophilic cells. Therefore it appears that this state of unresponsiveness is not exclusively conditioned by the absence of large pyroninophilic cells in paracortical areas and may be associated with other factors. [ABSTRACT FROM AUTHOR]

By determining the time and dose dependence of immuno-tolerance to dinitrochlorobenzene (DNCB) induced in guinea-pigs by previously injecting dinitrobenzenesulphonate (DNBSO3), it was found that smaller doses of DNBSO3 injected at short time intervals before the epicutaneous application of DNCB induced tolerance in fewer animals than higher doses. However, with small doses of DNBSO3, the percentage of tolerant animals increased the longer the time intervals between both hapten applications. A working hypothesis for this unexpected finding is proposed. [ABSTRACT FROM AUTHOR]