Susan J. Faas

Binding of antigen in the absence of histocompatibility proteins by arsonate-reactive T-cell clones

Inducer T-cell clones reactive to the p-azobenzenearsonate (arsonate) hapten possess binding sites for radioactive arsanylated proteins, which are not present on clones with other antigen specificities. Binding occurred in the absence of histocompatibility proteins. Binding was specific for the p-azobenzenearsonate hapten, since unconjugated proteins and proteins conjugated to the nonactivating o-azobenzenearsonate hapten neither bound to the clones nor competed binding of radioactive antigen. One of the clones was studied in more detail, using a panel of structural analogs of arsonate conjugated to the carrier protein ovalbumin. All conjugates that activated the clone in the presence of antigen-presenting cells also competed binding of radioactive antigen in the absence of antigen-presenting cells. Nonactivating conjugates did not compete binding. Based on evidence in this and the succeeding paper (Rao et al., accompanying paper), we suggest that these arsonate-binding sites may include the physiological antigen receptors of arsonate-reactive T-cell clones.

Analogs that compete for antigen binding to an arsonate-reactive T-cell clone inhibit the functional response to arsonate

We have tested several structurally related haptens, conjugated to ovalbumin, for their effect on activation of an inducer T-cell clone reactive to the p-azobenzenearsonate (arsonate) hapten. Low concentrations of some analogs inhibited DNA synthesis and lympkokine production by the clone in response to arsanylated antigen, but not in response to the lectin concanavalin A. Inhibition was specific for this clone, since the response of clones reactive to other antigens was not blocked. Inhibition may result from competition of these analogs with arsonate at a site on the T cell. The effectiveness of blocking by arsonate analogs parallels their ability to bind to a previously described arsonate-binding site on the clone (Rao et al., accompanying paper). We suggest that the binding and blocking assays detect the same physiological arsonate-recognition site on the clone, and hence that the cell-surface arsonate-binding sites we have described mediate its physiological response to antigen.

SV40 T-antigen is a histocompatibility antigen of SV40-transgenic mice

Although the extensive family of non-H-2 histocompatibility (H) antigens provides a formidable barrier to transplantation, the origin of their encoding genes are unknown. Recent studies have demonstrated both the linkage between H genes and retroviral sequences and the ability of integrated Moloney-murine leukemia virus to encode what is operationally defined as a non-H-2 H antigen. The experiments described in this communication reveal that skin grafts from an SV40 T-antigen transgenic C57BL/6 mouse strain are rejected by coisogenic C57BL/6 recipients with a median survival time of 49 days, which is comparable to those of many previously defined non-H-2 H antigens. The specificity of this response for SV40 T-antigen was demonstrated by the identification of SV40 T-antigen-specific cytolytic T lymphocytes and antibodies in multiply-grafted recipients. Although these cytolytic T lymphocytes could detect SV40 T-antigen on syngeneic SV40-transformed fibroblasts, they neither could be stimulated by splenic lymphocytes from T-antigen transgenics nor could they lyse lymphoblast targets from T-antigen transgenics. These observations suggest a limited tissue distribution of SV40 T-antigen in these transgenics. These results confirm the role of viral genes in the determination of non-H-2 histocompatibility antigenes by the strict criteria that such antigenes stimulate (1) tissue graft rejection and (2) generation of cytolytic T lymphocytes. Furthermore, they suggest that the SV40 enhancer and promoter region can target expression of SV-40 T-antigen to skin cells of transgenic animals.

Class I and class II restriction pattern polymorphisms associated with independently derived RT1 haplotypes in inbred rats

This communication reports the DNA level identification of class I and class II sequences associated with 20 RT1 haplotypes which have been assigned previously to eight RT1 groups. Sixteen to 22 bands in genomic blots hybridized with the mouse pH-2III class I cDNA probe. Only the three RT1khaplotypes associated with identical class I restriction fragment patterns. Differences in restriction bands between putatively identical RT1 haplotypes were either less than or equal to 6%, or greater than 50%, suggesting a relatively high level of recombination between serologically identified RT1.A genes and the majority of class I sequences. Restriction fragment patterns associated with three RT1uhaplotypes differed by less than 6%. However, intra-RT1a,intra-RT1b,and intra-RT1lrestriction fragment differences were between 50 and 64%. In specific cases, different RT1 haplotypes associated with identical class I restriction patterns, e.g., RT1m(MNR) and RT1d(MR); higher resolution confirmed the difference (two bands) between RT1mand RT1d.Results of hybridization with the human DC1βprobe confirmed that the AVN RT1aand NSD RT1bhaplotypes were generated by recombinations within the vicinity of the RT1.B : RT1.D regions. These results demonstrate that a previous classification of RT1 haplotypes was incomplete and did not include the majority of class I and class II sequences which distinguish RT1 haplotypes.

SV40 T Antigen Transgenic Mice: Cytotoxic T Lymphocytes as a Selective Force in Tumor Progression

The specific immune response to some antigenic determinants expressed on the initiated cell can be a contributing factor to the prevention of tumor appearance. Indeed, one aspect of tumor progression may be the evolution and selection of tumor cell variants capable of avoiding the immune response of the host. The oncogenic virus-induced tumors have provided the most direct evidence for these points; viral gene products elicit specific immune responses, and the normal cell-virus infected cell-virally transformed cell praxis provides an experimental system to test these concepts. However, in vivo tumorigenicity testing of cells transformed by viruses in vitro does not provide proof for these hypotheses since the characteristics of these cells following growth in vitro cannot reflect those of the analogous tumor cells arising in the selective environment of the intact organism. The development of the simian virus (SV40) tumor (T) antigen (ag) transgenic mouse1 has provided a model system in which the specific contribution, if any, of host immunity to the control of these endogenous tumors can be evaluated. Moreover, because expression of the viral transforming gene can be targeted to different tissues, by linking the sequences encoding the SV40 T/t antigens to those controlling transcription of other genes in specific cell types, a wide range of tumor types are available for comparison2–5. Expression of sufficient levels of the viral oncogene potentiates tumor formation but their appearance is controlled by subsequent events which may vary depending on the cell type and on the developmental time in which SV40 Tag is expressed.