Structural organization of the genes encoding human and murine FK506-binding protein (FKBP) 13 and comparison to FKBP1

FK506-binding protein (FKBP)12 and FKBP13 are members of a family of proteins which bind the immunosuppressant drugs, FK506 and rapamycin. FKBP12 and FKBP13 are encoded by distinct genes, designated FKBP1 and FKBP2, respectively. The structure of human FKBP1 was previously characterized. We now report the genomic structure of the human and murine FKBP2 genes. Comparison of FKBP1 and FKBP2 reveals significant homology and correlation of intron positions in the C-terminal region, suggesting that these genes may have evolved from a common ancestral gene.

The CD4 molecule is not always required for the T cell response to bacterial enterotoxins

T cells respond in a V beta-restricted fashion to bacterial enterotoxins bound to major histocompatibility complex (MHC) class II molecules. The requirement for CD4 in MHC class II-restricted T cell responses is very well established. We have assessed the role of CD4 in the T cell response to the bacterial enterotoxins Staphylococcal enterotoxin A (SEA), SEB, and toxic shock syndrome toxin 1. Three CD4- murine T cell hybridomas were transfected with the human CD4 molecule and assayed for interleukin 2 production in the presence of accessory cells bearing human MHC class II molecules and of the appropriate enterotoxin. The results clearly indicate that CD4- cells responded even to suboptimal concentrations of enterotoxin(s) equally well as CD4+ cells. Furthermore, expression of CD4 did not result in the acquisition of previously undetectable reactivity to enterotoxins. These results suggest that unlike the case with antigen-specific responses, formation of a T cell receptor-CD3/CD4 supramolecular complex is not always essential for T cell activation by bacterial enterotoxins.

Engraftment following T-cell-depleted marrow transplantation. I. The role of major and minor histocompatibility barriers

These experiments describe a murine model for survival and engraftment of bone marrow transplantation across differing histocompatibility barriers. Anti-Thy-1.2 antibody and complement-treated C57BL/6 (B6) marrow was transplanted at varying cell dose levels into syngeneic (B6), major histocompatibility complex congenic (A.BY), semiallogeneic (B6AF1), and fully allogeneic (A/J) recipients. Survival was monitored and engraftment determined by hemoglobin and lymphocyte phenotype. Survival was cell-dose dependent and was equivalent in B6, A.BY, and B6AF1 recipients. Survival was poor in allogeneic A/J recipients due to bone marrow failure even at high marrow dose levels. Survival posttransplant did not always correlate with stable donor engraftment, and competitive host marrow repopulation was frequently seen in B6AF1 recipients but rarely in A.BY recipients. This repopulation could be prevented by transplanting a larger marrow dose.

Antigen-specific suppression of cytotoxic T cell responses: an idiotype-bearing factor regulates the cytotoxic T cell response to azobenzenearsonate-coupled cells

When A/J mice are injected subcutaneously with azobenzenearsonate- (ABA) coupled spleen cells, their splenocytes contain primed ABA-specific cytotoxic T lymphocyte (CTL) precursors. Animals that are not primed in vivo do not develop vigorous CTL activity when assessed after in vitro culture with ABA-coupled stimulators. Suppressor molecules derived from ligand-induced first-order ABA-specific suppressor T cells were evaluated for their ability to limit cytolytic T cell development. We have shown that an idiotype-bearing, hapten-specific suppressor factor suppresses priming for CTL in an H-2-unrestricted but allotype-restricted manner. The implication of these studies to regulatory networks is discussed.

Antigen-specific suppression of cytotoxic T cell responses: an idiotype-bearing factor regulates the cytotoxic T cell response to azobenzenearsonate-coupled cells

When A/J mice are injected subcutaneously with azobenzenearsonate- (ABA) coupled spleen cells, their splenocytes contain primed ABA-specific cytotoxic T lymphocyte (CTL) precursors. Animals that are not primed in vivo do not develop vigorous CTL activity when assessed after in vitro culture with ABA-coupled stimulators. Suppressor molecules derived from ligand-induced first-order ABA-specific suppressor T cells were evaluated for their ability to limit cytolytic T cell development. We have shown that an idiotype-bearing, hapten-specific suppressor factor suppresses priming for CTL in an H-2-unrestricted but allotype-restricted manner. The implication of these studies to regulatory networks is discussed.

The origins of alloreactivity: differentiation of prekiller cells to viral infection results in alloreactive cytolytic T lymphocytes

Mice maintained in our animal colony become primed to Sendai virus. This "environmental" priming is reflected in a shift in prekiller activity from the Ly 123 to Ly 23 T cell set and in increased virus-specific cytolytic activity. This transition is accompanied by the development of cytolytic activity against allogeneic targets (not expressing Sendai antigens). These findings are consistent with the view that continued stimulation of Ly 123 cells by autologous MHC antigens, associated with foreign antigens such as a virus, generate Ly 23 prekiller cells that respond to alloantigens as well as autologous cells infected with the relevant virus.

The origins of alloreactivity: differentiation of prekiller cells to viral infection results in alloreactive cytolytic T lymphocytes

Mice maintained in our animal colony become primed to Sendai virus. This "environmental" priming is reflected in a shift in prekiller activity from the Ly 123 to Ly 23 T cell set and in increased virus-specific cytolytic activity. This transition is accompanied by the development of cytolytic activity against allogeneic targets (not expressing Sendai antigens). These findings are consistent with the view that continued stimulation of Ly 123 cells by autologous MHC antigens, associated with foreign antigens such as a virus, generate Ly 23 prekiller cells that respond to alloantigens as well as autologous cells infected with the relevant virus.

Major histocompatibility complex products restrict the adherence of cytolytic T lymphocytes to minor histocompatibility antigens or to trinitrophenyl determinants on schistosomula of Schistosoma mansoni

We have previously shown that schistosomula passaged through mice acquire histocompatibility (H) antigens that can be recognized either by alloantibody or by alloreactive cytolytic T lymphocytes (CTL). The latter specifically adhere to but fail to damage the parasite. In this paper we describe the use of trinitrophenyl (TNP)-labeled schistosomula to show that the adherence of CTL with specificity for TNP-modified syngeneic cells is restricted by the major histocompatibility complex (MHC) in a fashion similar to that seen in the lysis of TNP-labeled tumor targets. Thus, these CTL adhere only to schistosomula that have both the appropriate H antigens and TNP determinants on their surface, and not to schistosomula bearing either of these antigens by themselves. We note a significant degree of adherence to schistosomula bearing TNP determinants and H antigens allogeneic to the CTL. Anti-minor H antigen CTL are also restricted by the MHC in their adherence; thus, they only adhere to schistosomula that carry both the major and minor H antigens of the stimulator cells. These antigens can be acquired either by a single passage in vivo of schistosomula through congenic strains that possess both the relevant antigens or by sequential passage through two different strains, each contributing one of the antigens in question.

Induction of secondary cytotoxic T lymphocytes by purified HLA-A and HLA-B antigens reconstituted into phospholipid vesicles

Mouse cytotoxic T lymphocytes were induced by culturing primed spleen cells with cells, membranes, or detergent-solubilized and dialyzed membranes from the human lymphoblastoid cell line JY. Cytotoxic T cells could also be induced by coculturing primed spleen cells with phospholipid vesicles containing purified HLA-A and -B antigens derived from JY cells. The induction of killer cells by all subcellular fractions demonstrated an optimal response as a function of the amount of material added and, in the case of HLA-containing liposomes, this optimum was dependent upon the density of the HLA molecules in the liposomes. In addition, the maximal level of cytotoxicity elicited was also dependent upon this density. Finally, the cytotoxic cells demonstrated specificity as judged by a lower level of lysis on an HLA-unrelated lymphoblastoid cell line than on the appropriate target, JY. These results suggest that major histocompatibility antigens alone are sufficient for the induction of a secondary cytotoxic T lymphocyte response. It is proposed that this system may be useful in defining possible sites on the HLA molecule recognized by cytolytic T lymphocytes.

The induction of cytolytic T lymphocytes with purified plasma membranes

Subcellular fractions were demonstrated to be effective in stimulating primary and secondary allogeneic CTL responses. 5' nucleotidase activity was used to assess purification of plasma membranes and stimulating activity was found to co-purify with the plasma membrane fraction of the cell. Electron micrographs of these purified plasma membranes showed the majority of the material to be in the form of vesicles of relatively heterogeneous size. The cytolytic T lymphocytes generated by incubation with purified plasma membranes demonstrated immunologic specificity.

The induction of secondary cytolytic T lymphocytes by solubilized membrane proteins

Membrane-bound antigens responsible for induction of a secondary allogeneic murine cytolytic T-cell (CTL) response have been obtained in a soluble, biologically active form by deoxycholate solubilization of tumor cell plasma membranes. The active proteins are soluble by the criteria of both ultracentrifugation and gel filtration. The immunological specificity of the induced CTL and removal of the activity from solution by treatment with B6 anti-P815 (anti-H-2d) antiserum and Protein A-Sepharose demonstrate that the CTL-inducing activity is dependent upon solubilized major histocompatibility complex antigens.

Cytotoxic T lymphocytes induced against allogeneic I-region determinants react with Ia molecules on trinitrophenyl-conjugated syngeneic target cells

The major histocompatibility complex codes for determinants which are recognized by and serve as targets for cytolytic T lymphocytes (CTL) (1). Antigens coded for by the K and D loci of the H-2 complex can activate xenogeneic or allogeneic CTL (2,3). In addition, the H-2K or H-2D gene products function as those molecules against which syngeneic CTL responses specific for chemical, viral, and minor H antigens are directed (4-8). It has recently been shown that Ia determinants can also serve as target antigens for distinct but weaker CTL responses (9-13). Those clones which recognize Ia antigens see them independently of K- or D- coded antigens as shown in genetic studies and by antisera-blocking experiments (12,13). We have proposed that the existence of clones of CTL specific for I-region-coded determinants is not fortuitous; rather these clones specifically recognize Ia determinants and may have an immunoregulatory role. These CTL may affect those immune functions which are at least partially dependent on or controlled by I-region-coded molecules. Two predictions can be made and tested concerning the role of Ia determinants in cytolytic systems and the role, if any, of I-region- specific CTL in regulating the immune response: (a) that if as we and others have shown, certain Ia specificities can serve as a third series of major histocompatibility antigens, then Ia antigens should be susceptible to the same types of antigenic modifications as H-2K- or H-2D-coded structures and thus serve as targets for CTL directed against modified-self in selected systems; and (b) that allogeneically induced I-region-specific CTL should demonstrate cross-reactivity with targets bearing modified syngeneic I-region-coded determinants. Data will be present which demonstrates that trinitrophenyl (TNP)-modified syngeneic I-region determinants can serve as targets for CTL induced by allogeneic Ia antigens.

Cytotoxic T lymphocytes specific for I region determinants do not require interactions with H-2K or D gene products

Gene products coded for by the major hisocompatibility complex (MHC) can serve as target antigens for cytotoxic T lymphocytes (CTL) (1). A variety of test systems are available which have yielded information consistently reinforcing the importance of this complex of genes in the generation and effector phases of the cytotoxic immune response. Originally, it was shown that allogeneically-induced CTL had specificity primarily for the products of the K and D loci of the mouse H-2 complex (2). More recently this has also been found to be the case for xenogeneic immunizations (3,4). Additional examples of T cell-mediated lysis have been reported involving viral-infected or chemically- modified syngeneic stimulating and target cells in which homology at H-2K or H-2D was required between the responding and target cells for appreciable lysis to occur (5-7). Moreover, CTL specific for minor histocompatability antigens are able to lyse only target cells bearing these membrane antigens and sharing a common H-2K or H2-D gene product with the effector (8,9). Two hypotheses have been proposed to explain the requirement for H-2 identity between effector and targets in these systems. CTL may recognize new antigenic determinants created by the interaction of the modifier with syngeneic K and D gene products. Alternately, a dual recognition system my exist, requiring an antigen-specific receptor as well as a second receptor with specificity for homologous H-2K or H-2D determinants (5). Neither model can be excluded at this time. The I region also contains genes coding for histocompatibility loci since animals differing at the I-A or I-C regions of the H-2 complex reject skin grafts (10-12), though less rapidly than mice differing at the H-2K or H-2D regions, Also CTL can be generated to I region determinants but less efficiently than CTL specific for H-2K or H-2D gene products (12-14). The question can therefore be raised, whether the I region minor histocompatibility loci function independently from the H-2K or H-2D loci or whether I region-specific cytolysis requires the participation of H-2K or H-2D gene products of the target cell. This communication illustrates the generation of CTL showing specificity for I region determinants in primary mixed lymphocyte cultures. Further, we demonstrate by genetic analysis and byt eh use of speficit alloantisera that CTL directed to Ia determinants (a) do not see these antigens as modifications of H-2K or H-2D gene products but as independent gene products coded for by the I region, and (b) they do not require interaction with target cells bearing the same H-2K or H-2D gene product as the effect CTL.