CD8 T Cell Depletion, a Paradox

From these data it might be expected that removal of CD8 T cells would enhance IgE production and favour TH2-type immune responses. However, this appears to depend on the stage at which depletion is carried out. Thus, if CD8 T cells are depleted in rats (using the mAb OX-8) in which an IgE response had been induced, then the usual decline in serum IgE levels is prevented (Holmes etal., 1994). This supports the view that CD8 T cells suppress IgE. However, if depletion of CD8 T cells is performed prior to immunization, then the IgE response is not enhanced. Moreover, the IgE response is 

Discrepancies between the effects of 008 T cell depletion on the early and later stages of the immune response are not uncommon. In the mercuric chloride-induced model of autoimmune disease (Mathieson et al., 1991), 

CDS T cells might regulate IgE pioduction by suppressing IgE synthesis througji the inhibitory eflfect of IFN7 on B cells and/or by altering the diflFerentiation and function of TH2-like T cells. There is in vivo 

This treatment also results in a transient 10-fold increase in the capacity of splenocytes to produce the TH2-type cytokines IL-4, lL-5 and lL-10 (Noble et al., 1993c). Furthermore, adoptive transfer of early-activated IgE-specific 008 T suppressor cells enhances the production of IFN7 by splenocytra more than 1000-fold, although it is yet not clear if IFN7 is the product of the adoptively transferred CD8 donor cells or host 004 or CD8 T cells (Kemeny et al., 1994). 

These data suggest either that CDS T cells inhibit CD4 T cell development in an unrestricted manner, or that there were different populations of CD8 T cells that exerted differential effects on ThI and Th2 CD4 T cell development. Clearly, this will not be resolved until more CD8 T cells have been cloned and the effects of these clones on CD4 T cell development determined. The feet that immunoregulatory CDfl T cells appear to be active early in the immune response places these cells in an ideal position to influence the direction that the response will take. However, how CDS T cells are recruited and activated, how they interact with accessory cells and recognize antigen, and how they mediate their effects, have yet to be determined. 

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