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Biomedical subjects

L Polak

Publications and source records attributed to L Polak.

At least 37 records · Page 2Linked to original sources
PubMed1979

Induction of tolerance to DNCB-contact sensitivity in guinea pig fetuses.

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.

Aging↗
PubMed1978

Mechanism of densensitization in DNCB-contact sensitive guinea pigs.

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.

Animals↗
PubMed1978

Recent trends in the immunology of contact sensitivity. I.

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.

Dermatitis, Contact↗
PubMed1978

Persistent activity of suppressor cells in T cell-mediated immune response.

Tolerance to dinitrochlorobenzene contact sensitivity induced i.v. injection of dinitrobenzenesulfonic acid in guinea pigs is a long-lasting phenomenon (up to 1 year). The tolerogen, however, was traceable in the circulation only up to 3 months after its application. In spite of that, tolerance was adoptively transferred by parabiosis 6 months after being induced. Moreover, active suppressor cells eliminated by cyclophosphamide treatment are able to regenerate in those adoptively tolerized animals. These results indicate that the tolerogenic injection stimulates precursors of suppressor cells to generate active suppressor cells and memory cells of suppression. The further formation of active suppressor cells from memory cells seems to be tolerogen independent, but the existence of specific stimulator cells for suppression may be considered. These cells may bind undetectable small amounts of tolerogen. The recovery of suppression might, however, be also due to recovery of suppressor cells which were temporarily inactivated but not destroyed by cyclophosphamide treatment.

Animals↗
PubMed1977

Effect of the elimination of suppressor cells on the development of DNCB contact sensitivity in guinea-pig.

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.

Animals↗
PubMed1976

Mechanism of reappearance of contact sensitivity to DNCB in desensitized guinea pigs.

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.

Animals↗
PubMed1976

Studies on the role of suppressor cells in specific unresponsiveness to DNCB.

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.

Animals↗
PubMed1975

Differing mechanisms of tolerance and desensitization to dinitrochlorobenzene in guinea pigs.

In the present paper the mechanisms of tolerance and desensitization to dinitrochlorobenzene (DNCB) contact sensitivity in guinea pigs were investigated using the methods of adoptive sensitization of tolerant and normal syngeneic recipients and cyclophosphamide-treatment of tolerant animals known to selectively inactivate suppressor lymphocytes. It was shown that desensitization of presensitized animals is caused by the direct effect of the intravenously injected hapten on the effector cells in the peripheral compartment. The immediate onset of unresponsiveness and its very short duration almost exclude the possible involvement of enhancing antibodies or suppressor cells. In the case of tolerance induced by pretreatment with dinitrobenzenesulfonic acid, suppressor cell activity is enhanced, preventing normal specific immunocompetent cells from recognizing the antigen and/or proliferating in the draining lymph nodes. Whether suppressor lymphocytes are of the B or T type is not yet known.

Animals↗