Disparate Primary and Secondary Allospecific CD8+ T Cell Cytolytic Effector Function in the Presence or Absence of Host CD4+ T Cells

Abstract

The role of CD4+ T cells in promoting CD8+ T cell effector activity in response to transplant Ags in vivo has not been reported. We used a hepatocellular allograft model known to initiate both CD4-dependent and CD4-independent rejection responses to investigate the contribution of CD4+ T cells to the development, function, and persistence of allospecific CD8+ T cell effectors in vivo. Complete MHC-mismatched hepatocellular allografts were transplanted into C57BL/6 (CD4-sufficient) or CD4 knockout (CD4-deficient) hosts. The development of in vivo allospecific cytotoxicity was determined by clearance of CFSE-labeled target cells. CD8+ T cell cytotoxic effector activity was enhanced in response to allogeneic hepatocellular grafts with a greater magnitude of allocytotoxicity and a prolonged persistence of CTL effector activity in CD4-sufficient hosts compared with CD4-deficient hosts. Cytolytic activity was mediated by CD8+ T cells in both recipient groups. In response to a second hepatocyte transplant, rejection kinetics were enhanced in both CD4-sufficient and CD4-deficient hepatocyte recipients. However, only CD4-sufficient hosts developed recall CTL responses with an augmented magnitude and persistence of allocytotoxicity in comparison with primary CTL responses. These studies show important functional differences between alloreactive CD8+ T cell cytolytic effectors that mature in vivo in the presence or absence of CD4+ T cells.

Recipient Immune Repertoire and Engraftment Site Influence the Immune Pathway Effecting Acute Hepatocellular Allograft Rejection

“…Furthermore, the of hepatocyte transplant. These studies support the idea although antigen-specific CD8 + T cells have been shown to proliferate at the graft site during combined CD4 and that alloreactive CD8 + T cells can be activated to develop potent effector function at the graft site to cause CD8-dependent rejection, as well as in (CD4-independent) CD8 dependent rejection (23). It was interesting rapid rejection, but in the absence of CD4 + T cells, the amplification of CD8 + T-cell immunity is lessened, reto note that the inflammatory infiltrate was similar for each rejection pathway, unlike published reports showsulting in low-magnitude systemic in vivo cytotoxicity activity.…”

“…We also investigated the correlation of peripheral immune hosts (23). However, we have subsequently determined that the presence of high titer donor-reactive antibody monitoring of alloantibody, DTH, or in vivo cytotoxicity with activity of distinct rejection mechanisms, which correlates with the magnitude of in vivo cytotoxicity observed in these hosts (Horne, unpublished observation).…”

“…Allograft recipient mice and control naive mice received 20 × 10 6 get cells with naive C57BL/6 mouse serum or wash buffer during the primary incubation. Nonspecific bind-2), which is mediated by CD8 + T cells (23). In contrast, humoral immunity as reflected by donor-reactive IgG ing of the secondary antibody to target splenocytes (approximately 1%) was used to establish the background antibody is not detected (Fig.…”

“…Numrecipient mice were euthanized for excision of the liver bers of CD4 + and CD8 + T cells begin to rise by day or kidney, depending on engraftment route of the recipi-3 posttransplant and reach their peak levels at 7 days ent. The livers or kidneys were digested in a solution posttransplant, corresponding with the peak in vivo cycontaining 0.05% collagenase (Sigma, type IV) in 1% tolytic activity (23). All cell populations return to prealbumin for 10 min and cells were separated through transplant levels soon after allograft rejection (days 10-mechanical dispersion.…”

Alloreactive (CD4-Independent) CD8+ T Cells Jeopardize Long-Term Survival of Intrahepatic Islet Allografts

“…Neither DST and anti-CD154 mAb-treated C57BL/6 islet 'acceptor' mice or CD4-depleted C57BL/6 islet hepatocyte cotransplant rejector mice had alloantibody in recipient serum. Prior studies demonstrate that development of allospecific cytotoxicity after allogeneic hepatocyte transplant is CD8 + T cell mediated (46). These data indicate that local activation of CD8 + T-cell-dependent cytotoxic effector responses can precipitate islet allograft damage and/or disrupt survival of islet allografts even after long-term engraftment in the liver.…”