Mice lacking C1q or C3 show accelerated rejection of minor H disparate skin grafts and resistance to induction of tolerance

Complement activation is known to have deleterious effects on organ transplantation. On the other hand, the complement system is also known to have an important role in regulating immune responses. The balance between these two opposing effects is critical in the context of transplantation. Here, we report that female mice deficient in C1q (C1qa(-/-)) or C3 (C3(-/-)) reject male syngeneic grafts (HY incompatible) at an accelerated rate compared with WT mice. Intranasal HY peptide administration, which induces tolerance to syngeneic male grafts in WT mice, fails to induce tolerance in C1qa(-/-) or C3(-/-) mice. The rejection of the male grafts correlated with the presence of HY D(b)Uty-specific CD8(+) T cells. Consistent with this, peptide-treated C1qa(-/-) and C3(-/-) female mice rejecting male grafts exhibited more antigen-specific CD8(+)IFN-gamma(+) and CD8(+)IL-10(+) cells compared with WT females. This suggests that accumulation of IFN-gamma- and IL-10-producing T cells may play a key role in mediating the ongoing inflammatory process and graft rejection. Interestingly, within the tolerized male skin grafts of peptide-treated WT mice, IFN-gamma, C1q and C3 mRNA levels were higher compared to control female grafts. These results suggest that C1q and C3 facilitate the induction of intranasal tolerance.

Peripheral "CD8 tuning" dynamically modulates the size and responsiveness of an antigen-specific T cell pool in vivo

In this study, we suggest that CD8 levels on T cells are not static, but can change and, as a result, modulate CD8(+) T cell responses. We describe three models of CD8 modulation using novel weak-agonist (K1A) and super-agonist (C2A) altered peptide ligands of the HY smcy peptide. First, we used peripheral nonresponsive CD8(low) T cells produced after peripheral HY-D(b) MHC class I tetramer stimulation of female HY TCR transgenic and wild-type mice. Second, we used genetically lowered CD8(int) T cells from heterozygote CD8(+/0) mice. Finally, we used pre-existing nonresponsive CD8(low) T cells from male HY TCR transgenic mice. In CD8(low) and CD8(high) mice, presence of a lower level of CD8 greatly decreased the avidity of the peptide-MHC for HY TCR as reflected by avidity (K(D)) and dissociation constant (T(1/2)) measurements. All three models demonstrated that lowering CD8 levels resulted in the requirement for a higher avidity peptide-MHC interaction with the TCR to respond equivalently to unmanipulated CD8(high) T cells of the same specificity. Additionally, direct injections of wild-type HY-D(b) and C2A-D(b) tetramers into female HY TCR or female B6 mice induced a high frequency of peripheral nonresponsive CD8(low) T cells, yet C2A-D(b) was superior in inducing a primed CD8(+)CD44(+) memory population. The ability to dynamically modulate the size and responsiveness of an Ag-specific T cell pool by "CD8 tuning" of the T cell during the early phases of an immune response has important implications for the balance of responsiveness, memory, and tolerance.

DNA Fusion Vaccines Induce Targeted Epitope-Specific CTLs against Minor Histocompatibility Antigens from a Normal or Tolerized Repertoire

We have designed DNA fusion vaccines able to induce high levels of epitope-specific CD8(+) T cells, using linked CD4(+) T cell help. Such vaccines can activate effective immunity against tumor Ags. To model performance against minor histocompatibility (H) Ags important in allogeneic hemopoietic stem cell transplantation, responses against the H2D(b)-restricted Uty and Smcy male HY epitopes have been investigated. Vaccination of females induced high levels of tetramer-specific, IFN-gamma-producing CD8(+) T cells against each epitope. Vaccines incorporating a single epitope primed effector CTL able to kill male splenocytes in vitro and in vivo, and HY(Db)Uty-specific vaccination accelerated rejection of syngeneic male skin grafts. Priming against either epitope established long-term memory, expandable by injection of male cells. Expanded CD8(+) T cells remained specific for the priming HY epitope, with responses to the second suppressed. To investigate vaccine performance in a tolerized repertoire, male mice were vaccinated with the fusion constructs. Strikingly, this also generated epitope-specific IFN-gamma-producing CD8(+) T cells with cytotoxic function. However, numbers and avidity were lower than in vaccinated females, and vaccinated males failed to reject CFSE-labeled male splenocytes in vivo. Nevertheless, these findings indicate that DNA fusion vaccines can mobilize CD8(+) T cells against endogenous minor H Ags, even from a profoundly tolerized repertoire. In the transplantation setting, vaccination of donors could prime and expand specific T cells for in vivo transfer. For patients, vaccination could activate a potentially less tolerized repertoire against similar Ags that may be overexpressed by tumor cells, for focused immune attack.

Transplantation tolerance induced by intranasal administration of HY peptides

Induction of antigen-specific tolerance to transplantation antigens is desirable to control host-versus-graft and graft-versus-host reactions. Following molecular identification of a set of minor histocompatibility (H) antigens, we have used selected HY peptide epitopes for this purpose. Intranasal administration of individual major histocompatibility complex (MHC) class II-restricted HY peptides induces indefinite survival of syngeneic male skin grafts and allows engraftment of male bone marrow. Tolerance involves linked suppression to additional HY epitopes on test grafts. Long-term tolerance also requires suppression of emerging thymic emigrants. It does not involve deletion. HY peptide-specific CD4(+) and CD8(+) T cells expand on re-exposure to male antigen; these expansions are smaller in tolerant than control mice and fewer HY-specific cells from tolerant females secrete interferon gamma and interleukin 10 (IL-10). Significantly, CD4(+) cells from peptide-pretreated females fail to make IL-2 responses to cognate peptide, limiting expansion of the HY-specific CD8(+) populations that can cause graft rejection. Consistent with this, tolerance induction by HY peptide is abrogated by coadministration of lipopolysaccharide. IL-10 does not appear to be critically involved because tolerance is inducible in IL-10-deficient mice. Adoptive transfer of tolerance into naive neonatal recipients by splenocytes from long-term tolerant donors provides evidence for involvement of regulatory cells.

Failure to induce neonatal tolerance in mice that lack both IL-4 and IL-13 but not in those that lack IL-4 alone

Current evidence suggests that neonatal tolerance to a foreign Ag is the consequence of IL-4-mediated Th2 immunity rather than the thymic deletion of Ag-specific T cells. Here, we addressed the role of IL-4 in neonatal tolerance by testing whether tolerance to a minor histocompatibility Ag can be induced in newborn mice that lack IL-4 (IL-4(-/-)). We found that IL-4 does not play a dominant role in the induction of neonatal tolerance as newborn female IL-4(-/-) mice could be readily tolerized to the H-Y male Ag. In contrast, mice that lack both IL-4 and IL-13 (IL-4(-/-)/IL-13(-/-)) were resistant to the induction of neonatal tolerance, and their splenocytes produced exaggerated amounts of IFN-gamma on rechallenge with the same Ag encountered during the neonatal period. These findings argue against the view that IL-4 alone is critical for the induction of neonatal tolerance and suggest that the combined actions of both IL-4 and IL-13 are essential for this process.

Reduction of fertility in female rabbits and mice actively immunized with a germ cell antigen (GA-1) from the rabbit

Female rabbits and mice were actively immunized against germ cell antigen (GA-1) of 63 kDa molecular mass isolated from rabbit sperm and testis. There was a significant (P less than 0.05) reduction of fertility in rabbits actively immunized with GA-1 as compared to controls, as seen by the percentage of 9-day implants/corpora lutea ratio (GA-1, 36.3%; controls, 85.7%). In mice, there was again a significant (P less than 0.01) reduction in fertility as seen by mean 7-9 day implants +/- S.D. per mated mouse actively immunized with GA-1 whether through the intraperitoneal route (GA-1, 1.2 +/- 1.6; controls, 8.0 +/- 3.4) or through the subcutaneous/intramuscular route (GA-1, 3.8 +/- 3.4; controls, 10.1 +/- 3.9). The antisera from these actively immunized animals were negative for sperm agglutinating and immobilizing antibodies. In the Western blot enzyme-immunobinding procedure, the antisera showed specific binding to a single protein of 63 kDa. The incidence of fertilization of eggs recovered from rabbits inseminated with anti-GA-1 antibodies-treated sperm was not significantly different from control rabbits. The percentage of fertilized eggs obtained from rabbits inseminated with anti-GA-1 antibodies-treated sperm that reached the blastocyst stage upon in vitro incubation, however, was significantly less than that for embryos obtained from rabbits inseminated with control serum-treated sperm. Incubation of normal fertilized eggs in vitro with the antibodies did not affect development. Neither antiserum nor immune uterine fluid reacted with 4-day blastocysts in the indirect immunofluorescence technique. It is concluded that active immunization with GA-1 results in post-fertilization reduction of fertility in rabbits and mice by inhibiting early embryonic development.

Syngeneic spleen cell immunization induces high mortality among progeny in mice

Syngeneic spleen cell immunization of C57BL/6J females prior to syngeneic matings resulted in significant perinatal and postnatal mortality and increased abnormality among progeny. Thus female recipients of transplants and transfusions from major histocompatibility complex (MHC) compatible donors might effect some risk to their progeny.

H-Y antigen and immunity: a means for controlling the secondary sex ratio?

C57BL/6J female mice were splenectomized and then sensitized to the H-Y antigen by means of grafts of H-Y incompatible skin and injections of spleen cells from syngeneic males. When subsequently mated to syngeneic males the secondary sex ratio of progeny born was significantly greater than that of controls. However, the effect was manifest only among the progeny of later litters (i.e., 3, 4, 5) suggesting that repeated exposure to the H-Y antigen during the course of pregnancy was essential to bring about demonstrable immunoregulatory changes.

Cytotoxic T-cell response to H-Y in 'non-responder' CBA mice

Murine cytotoxic T-cell (Tc cell) responses to various antigens are controlled by immune response genes (Ir) mapping in the major histocompatibility complex (H-2). Both helper T cells, controlled by I region-coded genes, and Tc cells, controlled by K/D antigens, are necessary for a positive response. An H-2-restricted Tc-cell response to the male specific minor transplantation antigen (H-Y) can be elicited in B10 (H-2b) female mice primed with syngeneic male spleen cells intraperitoneally (i.p.) or intravenously (i.v.), or by skin grafting followed by restimulation in vitro in mixed lymphocyte culture (MLR) with male cells. CBA (H-2k) mice do not respond by these routes of in vivo priming, and this was thought to be due to a lack of permissible Ir genes for helper function. However, we now report that subcutaneous hind-footpad (fp) immunisation of 'non-responder' CBA mice with syngeneic male cells changes them to responders, a result which argues against a generalised Ir gene-controlled helper defect.