Role of antigen-presenting cells in the development and persistence of contact hypersensitivity.

Three outcomes pertinent to contact sensitivity (CS) follow immunization with various forms of trinitrophenylated (TNP) substrates: (a) specific immunological unresponsiveness for CS is induced when immunization favors activation of splenic suppressor cells. This state is achieved by intravenous injection of trinitrophenyl-conjugated to various types of cells, such as peritoneal exudate cells (PEC). (b) A short-lived or evanescent form of CS is induced when immunization reduces activation of the suppressor circuit. This can be achieved by subcutaneous immunization with trinitrophenyl conjugated to syngeneic PEC, by pretreatment with cyclophosphamide to diminish suppression before intravenous immunization, or by altering the mode of antigen presentation by using TNP-substrate that has undergone phagocytosis. (c) A long-lived form of CS is induced when trinitrophenyl is presented to the immune system on skin cells either by contact skin painting with reactive trinitrophenyl, or by subcutaneous, or even intravenous injection of trinitrophenyl-conjugated epidermal cells. In fact, trinitrophenyl-conjugated epidermal cells induced CS even when the suppressor circuit was activated by intravenous coadministration of TNP-PEC. This implies that antigen presentation on epidermal cells induces sensitized cells that are relatively resistant to suppression. The cell type(s) in the skin that are primarily responsible for this potent form of antigen presentation are most likely Langerhans cells, because they can be concentrated by virtue of their Fc receptors and they are Ia positive. Thus, both the anatomical site where antigen is first encountered by the immune apparatus, as well as the nature of the cells which present the antigen, determine whether a CS response will ensue, as well as whether it will be evanescent or long-lasting.

Induction of suppressor cells and cells producing antigen-specific suppressor factors by haptens bound to self carriers.

Injection of TNP-, DNP- or oxazolone-substituted syngeneic cells into mice causes the development of hapten-specific T suppressor cells which prevent the animals from being activity sensitized with homologous hapten. These cells injected together with immunized cells abrogate the latter's ability to transfer passively the contact sensitivity (CS) reaction into normal recipients. T lymphocytes from animals made unresponsive and sensitized with homologous hapten synthesize in vitro antigen-specific suppressor factors (SF) which when incubated with immune lymphocytes prevent them transferring adoptively the CS reaction. The type of cell used to induce suppression or production of suppressor factor (haptenated erythrocytes, thymocytes or macrophages) is not critical suggesting that a hapten-substituted common membrane structure is recognized as a tolerogen. The present work demonstrates that while the specific unresponsiveness induced by cell-bound hapten in vivo is long lasting, cells from tolerized animals are able to suppress the immunized cells in passive transfer or produce in vitro antigen-specific suppressor factors only when tested several days after tolerization.

Split unresponsiveness to trinitrophenyl (TNP) determinant. Suppression of anti-TNP antibody responses by sensitization with picryl chloride.

Contact sensitization by epicutaneous application of picryl chloride causes in mice a significant reduction of the antibody responses to immunogenic TNP-conjugates. This split unresponsiveness is along-lasting. It was found that hapten applied on the skin became attached to the serum proteins and the transfer of such a serum into normal recipients, while not influencing the ability of these animals to become contact-sensitized to PCl, rendered them unable to mount the anti-TNP antibody response. Possible mechanisms of split unresponsiveness to the TNP determinant induced by PCl treatment are suggested.

Split unresponsiveness to the trinitrophenyl determinant. I. Manoeuvers which suppress either humoral or cell-mediated immune responses.

2,4,6-Trinitrobenzene sulfonic acid (TNBS) injected intravenously (i.v.) makes mice fully tolerant to the trinitrophenyl (TNP) determinant. Administration of in vitro TNP-labeled syngeneic erythrocytes or thymocytes renders mice unable to develop contact sensitivity to picryl chloride, while the humoral anti-TNP responses seem to be unaffected. The reverse was found after pretreatment of mice with TNP-labeled isologous IgG (MGG) since only anti-TNP antibody responses, but not contact sensitivity to picryl chloride, were significantly reduced. TNP-coupled macrophages given to animals suppressed both the cell-mediated and humoral responses, and this might be due to the presence on their surface of TNP-labeled cytophilic antibody. TNBS administered i.v. binds to circulating proteins and formed blood elements. Thus the split unresponsiveness affecting either humoral or cell-mediated compartments after the injection of TNP-MGG or of haptenated cells respectively, is presumably due to dissecting events which in vivo after the injection of TNBS, occur simultaneously. These results may be interpreted to indicate that split unresponsive states to TNP determinants are mediated two independent mechanisms which require different tolerogen presentations to be triggered.

Impaired antibody responses in alloxan diabetic mice.

Alloxan diabetic BALB/C mice with high hyperglycaemia levels (larger than or equal to 600 mg/100 ml) when immunized either with T-dependent (SRCB) or T-independent (TNP-LPS) antigens show a significant decrease in the number of specific PFC when compared with normo-glycaemic controls. Moderate diabetes (greater than 350 mg/100 ml) does not affect the immune response and in some experiments a slight increase of anti-SRBC plaques was seen. In transfer experiments primed spleen cells of either diabetic or normal doners gave much better responses when transferred to normal rather than diabetic X-irradiated recipients. In Mishell-Dutton (MD) cultures anti-SRBC response of CBA spleen cells was moderately reduced only when the blood glucose level of cell donors exceeded 500 mg/100 ml. Glucose added to MD cultures of normal spleen cells diminished significantly the number of SFC when in concentrations exceeding 600 mg/100 ml. The data indicate that in diabetic animals B-lymphocyte function may be affected but give no clear-cut answer to whether this is also true for T-helper cells. Disabled lymphocytes, whatever population they represent, may partially recover when transferred into normo-insulinic milieu. It may be inferred that under conditions tested neither hyperglycaemia nor excess of corticosteroid accounted significantly for the impaired humoral responses in diabetic animals. These experiments imply, however, that in hypoinsulinaemia the lack of saturation of insulin receptors on the lymphocyte, and possibly also macrophage, membranes renders these cells functionally inactive presumably due to accumulation of cyclic AMP in the cell membrane.