Cellular and molecular events in the delayed-onset hypersensitivities

Specific Lyt 123 cells are involved in protection against Listeria monocytogenes and in delayed-type hypersensitivity to listerial antigens.

“…Because effector T cells mediating DTH reactions to SRBC and fowl gamma globulin have been reported to be phenotypically Lyt 1+23 - (9,12,13), our data imply either that particular T-cell functions are not restricted to particular Lyt T-cell subpopulations or that different kinds of antigen induce different pathways of T-lymphocyte activation, or both (14,15). The participation of Lyt 123 + T cells in DTH generated during the course of an infection can be taken as further evidence for the existence of two pathogenetically distinct types of DTH postulated for a long time (16): in one type of DTH, which is evanescent and is induced by nonin~fectious agents such as SRBC (Jones-Mote type), Lyt 1+23 -T cells participate, whereas in the other type, which is induced by intracellular bacteria (tuberculin-type), mainly Lyt 123 + T cells are involved.…”

Histopathology of Delayed-Onset Hypersensitivities in Contact-Sensitive Guinea Pigs

“…It seems reasonable to conclude that use of the terms 'tuberculin-type hypersensitivity' and 'cu taneous basophil hypersensitivity' for various de layed-onset hypersensitivities in a single guinea pig may be confusing and might be replaced by designat ing skin reactions as delayed-onset reactions contain ing many or few basophils, and mediated by T cell or antibody-dependent mechanisms [2,22], Even though histological examination of the tis sues involved in delayed-onset hypersensitivities can not define the underlying mechanisms that initiate these reactions, it can be of great value for under standing the final common pathways involved in tis sue pathology. The increased resolution obtained us ing 2-,urn sections of glycol methacrylate embedded tissues is an advantage which is not available with thicker paraffin sections.…”

“…Both mononuclear (lymphocyte, monocyte-macrophage) and granulocytic (neutrophil, eosinophil, basophil) elements have been recognized in the cellular infil trate [1][2][3][4][5][6][7]. In general, basophils are more prominent in contact reactions than in reactions elicited by PPD, while neutrophils are more evident in PPD reactions than in contact reactions [1][2][3].…”

“…However, reactions elicited by conjugates are more cross-reactive in comparison with those elicited by contact sensitizers. This may in dicate that these histologically similar responses de pend on different immune components such as anti bodies versus T cells [2,[9][10][11],…”

The control of the immune response: the significance of network theories.

“…These effects of complexes themselves form an elegant feedback loop to control antibody formation. Type IV reactivity is just the activity of the DTH class of T cells, considered in isolation from the other classes, and from other mechanisms which can produce what we now call a delayed onset hypersensitivity (Godfrey and Gell, 1978). There are therefore multiple ways of either promoting or damping down the immune response; in effect, all options are left open, and any stimulus can provide a positive or a negative effect according to circumstances.…”