RT1-U: identification of a novel, active, class Ib alloantigen of the rat MHC.

In common with other mammalian species, the laboratory rat (Rattus norvegicus) expresses MHC class I molecules that have been categorized as either classical (class Ia) or nonclassical (class Ib). This distinction separates the class Ia molecules that play a conventional role in peptide Ag presentation to CD8 T cells from the others, whose function is unconventional or undefined. The class Ia molecules are encoded by the RT1-A region of the rat MHC, while the RT1-C/E/M region encodes up to 60 other class I genes or gene fragments, a number of which are known to be expressed (or to be expressible). Here we report upon novel MHC class Ib genes of the rat that we have expression cloned using new monoclonal alloantibodies and which we term RT1-U. The products detected by these Abs were readily identifiable by two-dimensional analysis of immunoprecipitates and were shown to be distinct from the class Ia products. Cellular studies of these molecules indicate that they function efficiently as targets for cytotoxic killing by appropriately raised polyclonal alloreactive CTL populations. The sequences of these class Ib genes group together in phylogenetic analysis, suggesting a unique locus or family. The combined serological, CTL, and sequence data all indicate that these products are genetically polymorphic.

Novel HY peptide antigens presented by HLA-B27.

We have identified two peptides corresponding to the male-specific HY minor histocompatibility Ags presented by HLA-B27 in transgenic rodents, isolated from whole cell extracts and from immunoprecipitated B27 molecules of male B27 rat spleen cells. HPLC peptide fractions that sensitized female B27 targets for lysis by B27-restricted anti-HY CTL were analyzed by electrospray tandem mass spectrometry using a new highly sensitive quadrupole/time-of-flight instrument. Two peptide sequences were obtained, KQYQKSTER and AVLNKSNREVR. Synthetic peptides corresponding to these sequences bound B27 in vitro and were recognized by distinct B27-restricted anti-HY CTL populations. Neither peptide sequence entirely matches known protein sequences or shows a resemblance to known Y chromosome genes, but both show homology to known autosomally encoded proteins. Both peptides were shown to be controlled by the Sxr(b) segment of the short arm of the mouse Y chromosome, a segment known to contain all previously identified HY Ags. Taken together, these findings suggest that the two peptides arise as a result of Y chromosome-regulated control of one or more autosomal gene products. Although arginine at position 2 is a dominant anchor residue for peptides bound to B27, neither B27-presented HY sequence contains this residue. These studies, employing sensitive new methodology for identification of MHC-bound peptides, significantly extend the complexity of the genetic basis of HY Ags and expand the repertoire of antigenically active peptides bound to B27.

T cell suppression in transplantation tolerance through linked recognition.

Allogeneic tissues transplanted to mice treated with CD4- and CD8-specific Abs are often accepted indefinitely due to the induction of immunologic tolerance. When transplantation tolerance was induced to grafts mismatched at multiple minor histocompatibility loci, Ag specificity was inferred because third party grafts, mismatched at the MHC, were rejected normally. However, some "third party" grafts were either accepted, or rejected more slowly. Tolerant mice possess CD4+ cells, which suppress rejection by T cells reacting to the same grafts. Therefore, we hypothesized that tolerated third party grafts might share Ags with the original tolerizing graft, and that these Ags are a target for such suppression. To test this idea, we tolerized mice to a set of minor Ags (B10 minors) and challenged them with third party grafts that carried those minors, as well as an additional strong transplantation Ag, the class I MHC molecule, H-2Kb. This class I molecule acts as a good target for rejection in both naive mice and in mice tolerized to B10 minors. However, when this third party class I molecule is provided "linked" to those B10 minors on an F1 graft, rejection was significantly impaired. The data suggest that suppression within tolerant animals operates locally (perhaps on the same APC) via linked recognition. In addition, our preliminary findings suggest that suppression via linked recognition can also lead to tolerance to the third party Ag.

Rat MHC-linked peptide transporter alleles strongly influence peptide binding by HLA-B27 but not B27-associated inflammatory disease.

Rats transgenic for the human MHC molecule HLA-B27 were used to study the effect of two alleles, cima and cimb, which are associated with peptide transport by the MHC-encoded Tap2 transporter, on the function of HLA-B27 as a restriction element for CTL recognition of the male H-Y minor H Ag and on the multisystem inflammatory disease characteristic of B27 transgenic rats. Anti-H-Y CTL generated in cima B27 transgenic rats lysed male B27 cimb/b targets significantly less well than cima/a or cima/b targets. Addition of exogenous H-Y peptides to male B27 cimb/b targets increased susceptibility to lysis to the level of cima/a targets. Male B27 cimb/b cells were less efficient than cima/a cells in competitively inhibiting CTL lysis of female B27 cima/a targets sensitized with exogenous H-Y peptides. 3H-Labeled peptides eluted from B27 molecules of lymphoblasts from rats of two cimb and three cima RT1 haplotypes showed that the cimb peptide pool favors comparatively longer and/or more hydrophobic peptides. These results indicate that RT1-linked Tap2 polymorphism in the rat strongly influences peptide loading of HLA-B27. Nonetheless, the prevalence and severity of multisystem inflammatory lesions were comparable in backcross rats bearing either cima/b or cimb/b. It thus appears either that binding of specific peptides to B27 is unimportant in the pathogenesis of B27-associated disease or that the critical peptides, unlike H-Y and many others, are not influenced by Tap transporter polymorphism.

Undetectable levels of serum FSH immunoactivity and bioactivity in girls with sexual precocity due to ovarian cysts.

Clinical presentation and endocrine investigations in five girls with precocious sexual development due to ovarian cysts are presented. These girls had pubertal oestradiol and suppressed gonadotrophin responsiveness to LHRH stimulation. FSH bioactivity as measured by the rat aromatase assay was undetectable in basal and LHRH-stimulated serum samples but our results cannot exclude the possibility of the presence of a species-specific follicle stimulating factor in these patients. IM injection of depot medroxyprogesterone acetate controlled pubertal development in two children.

Classical transplantation tolerance in the adult: the interaction between myeloablation and immunosuppression.

Allogeneic bone marrow transplantation in the neonate is an effective way of inducing permanent tolerance to donor tissue. To do the same in the immunocompetent adult requires immunosuppression to counter host-versus-graft alloreactivity. Conditioning with monoclonal antibodies (mAb) to CD4 and CD8 has been sufficient where donor and recipient are mismatched at only multiple "minor" histocompatibility loci, or at major histocompatibility complex (MHC) class I plus "minor" loci, but not where the mismatch involves the entire MHC. Tolerance across the MHC barrier requires extra conditioning with agents that happen to be both immunosuppressive and myeloablative, so obscuring the assessment of which effect is important. By using dimethylmyleran as a selective "space"-creating myeloablative agent, and CD4 plus CD8 mAb as sole immunosuppressive agents, we have been able to dissect the relative requirements for immunosuppression and myeloablation. We show here that transplantation tolerance could only be achieved when both types of agent were combined together so as to guarantee sufficient donor-type hemopoietic chimerism. We argue that the donor marrow, given sufficient space, will engraft and provide a sustained source of tolerogen overriding any host resistance that antibodies cannot control.

How I use coal tar in dermatology.

Coal tar has been used in dermatology for over a hundred years. It was the main therapeutic agent for the treatment of various skin orders before the introduction of topical steroid. Since the advent of topical steroid the use of coal tar has reduced considerably. It is still being used a lot in the treatment of psoriasis. In this paper I will describe how I use coal tar not only in psoriasis, which is well known, but also in acne, folliculitis, eczema and seborrheic dermatitis and vitiligo, which are less well known.