The cellular mechanism of maintenance of neonatally induced tolerance to H-2 class I antigens

We used limiting dilution analysis protocols to investigate the mechanism by which in vitro cytotoxic T lymphocyte (CTL) hyporeactivity is maintained in adult mice that had been neonatally tolerized to major histocompatibility complex-encoded antigens. Class I molecules, presented on donor cells having an H-2 K or D region haplotype difference from recipients, readily induce tolerogen-specific CTL hyporeactivity. All attempts to identify any in vitro effects of active suppressive cells operative in the maintenance of this hyporeactivity have been unsuccessful. We conclude that this cytotoxic deficiency is the consequence of in vivo mediated clonal inactivation of the precursors of tolerogen-specific CTL. A presentation and evaluation of the assumptions inherent in this conclusion are made. In contrast to class I molecules, class II molecules, presented on donor cells having an H-2 I region haplotype difference from recipients, are unable to induce tolerogen-specific CTL hyporeactivity, even when injected neonatally at high doses. This inability of class II molecules to induce CTL tolerance parallels the considerable difficulty of inducing helper T lymphocyte tolerance to class II molecules.     

Basement membrane chondroitin sulfate proteoglycans: localization in adult rat tissues

Heparan sulfate proteoglycans have been described as the major proteoglycan component of basement membranes. However, previous investigators have also provided evidence for the presence of chondroitin sulfate glycosaminoglycan in these structures. Recently we described the production and characterization of core protein-specific monoclonal antibodies (MAb) against a chondroitin sulfate proteoglycan (CSPG) present in Reichert's membrane, a transient extra-embryonic structure of rodents. This CSPG was also demonstrated to be present in adult rat kidney. We report here the tissue distribution of epitopes recognized by these MAb. The ubiquitous presence of these epitopes in the basement membranes of nearly all adult rat tissues demonstrates that at least one CSPG is a constituent of most basement membranes, and by virtue of its unique distribution is distinct from other chondroitin and dermatan sulfate proteoglycans previously described.     

Blood supply of the upper craniofacial skeleton: the search for composite calvarial bone flaps

This study investigated the blood supply of the upper craniofacial skeleton by injection studies. The major supply to the calvaria is provided by the middle meningeal artery and its branches. This vessel is difficult for the plastic surgeon to exploit in composite bone-flap design. The majority of the outer surface of the craniofacial skeleton is supplied by tiny perforators from the overlying periosteum. The vascular interconnections within the periosteum are poorly developed. For this reason, the galea and the overlying vascular network (derived from the superficial temporal, occipital, supraorbital, and supratrochlear vessels) should be left broadly attached to the bone when transferring a vascularized calvarial bone flap. Dissection of the scalp away from this vascular network should be carried out just below the hair follicles. By observing these principles, vascularized calvarial bone can be transferred on the superficial temporal, deep temporal, supraorbital, supratrochlear, or occipital vessels. Details of the use of each are discussed.     

Evaluation of antibody inhibition assays of melanoma antigens in sera to monitor tumor growth in melanoma patients

Summary It was reported previously that melanoma leukocyte-dependent antibody (LDA) in the sera of melanoma patients was inhibited by small-molecular-weight (small-mol.-wt.) glycoproteins which were similar to cell surface antigens identified in cell membrane extracts of melanoma cells. The present study was to determine whether measurement of the levels of these factors in sera may be a useful monitor of tumor growth in melanoma patients. Small-mol.-wt. fractions were obtained by gel filtration or membrane chromatography of acidified sera and tested for their ability to inhibit LDA in ⁵¹Cr release cytotoxic assays. A panel of LDA was used, consisting of three antisera from melanoma patients, which appeared relatively specific for melanoma, and three non-melanoma antisera against carcinoembryonic antigen, ₂ microglobulin, and fetal antigens. The results showed that in patients with melanoma, approximately 70% had melanoma LDA-inhibitory activity detected in the small-mol.-wt. fractions of their sera when these were tested against the panel of melanoma LDA. The specificity of the inhibitory activity for melanoma LDA was shown by failure of the serum fractions to inhibit non-melanoma LDA and by absence of inhibitory activity in equivalent serum fractions from non-melanoma carcinoma patients for melanoma LDA. The levels of melanoma LDA-inhibitory activity in the serum fractions appeared to correlate with tumor growth, as shown by clearance of the inhibitory activity after surgical removal of melanoma and reappearance in the serum of patients who subsequently developed recurrent melanoma. The 30% false-negative rate indicated that the assays could not be used to reliably exclude melanoma, but the close correlation with tumor growth and the low number of false-positive results suggested that in 70% of patients detection of these small-mol.-wt. antigens would be of value to detect recurrence from melanoma and to monitor the effectiveness of therapy.     

Modulation of Ca2+ channels by atrial natriuretic peptide in the bovine adrenal glomerulosa cell.

In the bovine adrenal glomerulosa cell, calcium influx through voltage-dependent calcium channels is critical to maintaining an aldosterone secretory response. In patch clamp, atrial natriuretic peptide (ANP) inhibits T-type calcium channel current yet stimulates L-type calcium channel current. In the present study the channel effects of ANP observed in the patch-clamp configuration were extended and related to populations of cells. We observed the following. (i) The effect of ANP on T-channel current resulted in the reduction in the open state probability. ANP decreased the mean open state duration from 14.2 to 1.8 ms/sweep. (ii) In the weakly depolarized cell stimulated by 8 mM K+, ANP reduced the level of aequorin luminescence (a measure of cytosolic calcium) and completely inhibited the stimulated rate of aldosterone secretion, returning it to prestimulation values. These effects are consistent with a decrease in net calcium channel influx and the reported inhibition of T-channel current. In contrast, the calcium channel blocker, nitrendipine, which at low dose selectively blocks L-type calcium channel flux, only slightly reduced luminescence, and partially inhibited the sustained secretory response. (iii) In the strongly depolarized cell, stimulated by 60 mM K+, ANP increased the level of aequorin luminescence consistent with an increase in net calcium channel influx and the reported stimulation of L-channel current. These results indicate that under physiological conditions the inhibition of T-type calcium channels may be involved in the inhibition of the aldosterone secretion induced by ANP.     

On the defence strategy of Physa fontinalis (L.), a freshwater pulmonate snail

Summary Physa fontinalis (L.) gives a characteristic, chemically mediated escape response when stimulated by the majority of British leeches and flatworms. The snail responds rapidly and consistently to contact with all the molluskivorous leeches but also to three species which may be considered harmless. However, no response was given to Erpobdella octoculata, the most abundant and widespread of the harmless leeches. The flatworms generally evoked less strong reactions. The adaptive significance of the pattern of responsiveness is discussed. A weaker shell-shaking response is elicited in conspecifics and it is shown that this antisocial behaviour leads to a relatively spaced-out dispersion pattern. A possible adaptive advantage is the reduction of risk of detection by shell-crushing fish predators, to which the snails are otherwise extremely vulnerable.     

Histone-histone interactions within chromatin. Crosslinking studies using ultraviolet light.

Irradiation of either whole cells or chromatin at 280 nm results in the covalent linkage of histones 2A and 2B, presumably at their mutual binding sites. The reaction is specific and proceeds with high yield (about 80%). Irradiation of reconstituted nucleohistone containing only H2A, H2B and DNA also yields the H2A-H2B dimer. The cross-linking event is sensitive to the conformation of the H2A-H2B pair since the histones must be bound to DNA for maximum cross-linking specificity at low ionic strength. However, the histones must first interact with each other before being deposited on the DNA, since separate addition of the histones to the DNA yields no dimer upon irradiation. If irradiation is conducted at 254 nm rather than 280 nm, DNA-histone cross-linking appears to dominate.