Where are tomorrow's specialists?

AIM: To determine the extent to which New Zealand's future specialists are likely to be graduates of this country's medical schools. METHODS: Forward projections were made on the basis of information from: (1) Medical Council annual reports recording additions to the Register of Specialists between July 1 1990 and June 30 1994, (2) Medical Council annual questionnaire data relating to New Zealand doctors qualifying in 1971-85, (3) Medical Directories of Australia, Canada, UK and USA, (4) selected Australasian specialist colleges on the number of registered trainees in New Zealand, and (5) Medical School data on New Zealand graduating classes since 1971. RESULTS: Forty percent of the new specialists registered in New Zealand between 1 July 1990 and 30 June 1994 were graduates of overseas medical schools. Future projections suggest that this percentage is likely to increase. Major determinants of New Zealand specialist numbers are (1) the proportion of specialist New Zealand graduates (38%) not working in this country, and (2) the sex ratio of future graduating classes--proportionately fewer women (38%) than men (56%) specialise. CONCLUSION: Graduates of this country's medical schools are likely to supply approximately half of New Zealand's future specialists.

Evidence that changes in expression of major histocompatibility complex antigens may underlie the immunosuppressive effect of heat-treated cells in vivo and in vitro.

The prior transfusion of heat-treated (60 degrees C for 1 hr) allogeneic spleen cells is known to bring about specific prolongation of the survival of subsequent donor strain heart allografts. In this communication we show that some polymorphic and monomorphic class 1 determinants on spleen cells are heat denatured so that they no longer provoke antibody formation in naive allogeneic hosts. By contrast, the heated cells remain able to provoke the formation of anti-class 2 antibodies. When measured in a binding assay, the levels of anti-class 2 antibodies are similar irrespective of whether the immunizing inoculum consists of normal or heated cells. In a cytotoxic assay, the antibodies produced following exposure to normal cells are cytotoxic; this activity is substantially reduced when the cellular immunizing inoculum is heated. Cells heated to 60 degrees C for 1 hr are unable to stimulate in a mixed lymphocyte reaction, but reactivity can be partially restored by the addition of exogenous IL-2 to the culture. From previous evidence it seems unlikely that suppressor cells play a major role in the immunosuppression effected by cells heated to 60 degrees C. The results presented in this communication suggest a possible role for anticlass 2 antibodies and also imply the defective production of a costimulatory signal that normally follows the presentation of allogeneic MHC antigens.

The F1 hybrid effect in allogeneic lymphocyte cytotoxicity. Points of similarity between hybrid resistance and ALC.

Allogeneic lymphocyte cytotoxicity (ALC) is characterized by the rapid destruction of intravenously injected allogeneic lymphocytes by unsensitized hosts. While ALC has been reported in several mammalian species, it has been most extensively studied in rats. All the available in vivo and in vitro evidence points to NK cells as the effectors of ALC. The experiments described in this communication show that when donor and host share common ALC determinants, the extent to which allogeneic lymphocytes are killed is greatly reduced, and sometimes even abolished, relative to the killing that would have occurred in the absence of shared determinants. Thus, allogeneic lymphocyte transfers in inbred rat strain combinations having the general pattern A----B are associated with significantly higher levels of ALC than are the corresponding (A x B)F1----B, A----(A x B)F1 or (C x A)F1----(C x B)F1 lymphocyte transfers. The reduced ALC is not due to inability of the F1 hybrid to respond with the full vigor of the parental strains. Nor is it due to an absolute requirement for homozygous presentation of the donor ALC determinants. It is concluded that impaired self-recognition may be an important determinant of killing in ALC, as in some other NK cell-mediated phenomena. Although ostensibly differing immunogenetically from hybrid resistance in mice, ALC includes a range of patterns of reactivity, some of which are similar to those that characterize hybrid resistance. It is suggested that hybrid resistance and ALC may represent quantitative variants of a similar process.

A proposed growth regulatory function for the serologically detectable sex-specific antigen H-Ys.

It is widely believed that the serologically detectable sex-specific antigen H-Ys plays a major role in the primary determination of sex. The cellular distribution of the antigen, however, seems to be at odds with its postulated function. Consideration of this apparent paradox has prompted the suggestion that the H-Ys antigen functions as a growth regulator, and that its role in the primary determination of sex can be accounted for on this basis. Circumstantial evidence is adduced that H-Ys is a growth regulator in the embryo, and this is supported by evidence from several sources not immediately related to embryonic growth or development. Genes coding for growth regulators can function as oncogenes in situations involving disordered regulation, and it is suggested that this accounts for the high incidence of ovarian neoplasms in H-Ys positive, but not in H-Ys negative, female patients with 46,XY gonadal dysgenesis (Swyer's syndrome). A postulated growth regulatory function of H-Ys lends weight to the contention of others, not only that the direction of differentiation of the indifferent gonad in the embryo is determined by its growth rate, but also that a common mechanism underlies genotypic sex determination and environmental sex determination.

The distribution of sex-specific (H-Y) antigens within the seminiferous tubules of the testis: an immunohistochemical study.

The cellular distribution of H-Y antigen within the seminiferous tubules of testes from both 20-day-old and adult rats has been examined immunohistochemically. Large amounts of diffuse-staining material surrounding the germ cells were observed within the tubules of 20-day-old rats while the germ cells appeared to have little H-Y positive material on them. In the sexually mature rat, the seminiferous tubules contained cells at various stages of development. Peroxidase staining was evident on many, but not all of these cells. On spermatids and spermatozoa with cytoplasmic droplets attached, peroxidase staining appeared to be present in only a proportion of these cells.

Immunosuppressive activity of class I antigens in the absence of antigen-presenting cells that are MHC-compatible with the host.

Pretransplant transfusions of heat-treated spleen and lymph node cells were shown to prolong the survival of DA strain heart grafts in 3 allogeneic host strains: BS, HS, and AS2. To examine whether MHC incompatibility was necessary for immunosuppression mediated by heat-treated cells, AS strain skin-graft recipients were pretreated with fresh or heated inocula from either MHC compatible or incompatible congenic donor strains, AS2.1L(AS) and AS.1F(AS2) prior to transplanting donor strain skin. Prolonged survival was observed only in the MHC-incompatible strain combination, and in this MHC-incompatible strain combination, and in this instance heated cells were conspicuously more immunosuppressive than fresh cells. To determine the effect of intra-MHC differences between donor and host on graft survival, cells from a recombinant donor strain (r22), which shared class II antigens with the graft donor strain and class I antigens with the host, were transfused prior to heart transplantation. Neither fresh nor heated r22 cells prolonged graft survival. Our data accord with the suggestion that in the absence of MHC-compatible antigen-presenting cells, foreign class I antigen is immunosuppressive.

Identification of a male-specific (H-Y) antigen on the flagellar plasma membrane of ram epididymal spermatozoa.

H-Y (male-specific) antigen has been detected on the plasma membranes of both caput and caudal ram spermatozoa using both immunoperoxidase and immunofluorescence labelling techniques. In these spermatozoa the distribution of H-Y antigen appears to be confined to both the posterior region of the head and the mid-piece region of the flagellum. In addition, caput spermatozoa also exhibit intense immunoperoxidase staining of the cytoplasmic droplet which is situated on the flagellum at the base of the head. Western blot analyses of purified plasma membranes from the flagella of caudal spermatozoa have revealed the presence of a male-specific protein with an estimated molecular weight of 25,000-27,000.

For better or for worse? Women doctors at the end of the decade.

The position of women doctors at the beginning of the UN Decade for Women (1976-1985) is compared with their position at its end. In 1985 women made up over 20% of all practising doctors, 34% of the house surgeons, 27% of the registrars and 27% of the psychiatric specialists in New Zealand. While women now make up half of the second year entrants at the University of Otago, they account for only a small proportion of the teachers. At Dunedin the proportion of women teachers has changed little over the decade. Indeed, if psychiatrists are excluded, the proportion of women teachers is slightly lower at the end of the decade than in 1975, 1965 or 1955. Several major university departments at Dunedin-general practice, obstetrics and gynaecology, paediatrics and surgery-list no women clinical teachers. The position is much the same at the Christchurch and Wellington clinical schools. Half of the women teachers at the three University of Otago schools are psychiatrists. Among hospital specialists in New Zealand men are about three times as likely as women to be promoted above the bar in the specialists' salary scale. The present system of postgraduate training effectively culls many of the women doctors who have children before they have acquired a postgraduate qualification, by severely limiting their subsequent career options. The same system encourages women doctors to have their children late, and probably deters some medical women from having children at all. Many Dunedin women students entering 2nd year classes in Dunedin are unaware of the potential problems which they may encounter at postgraduate level.

An immunochemical procedure for the purification of rat class I antigens (RT1.A/RT1.E) from detergent-solubilized erythrocytes.

An immunochemical procedure using two immunoaffinity columns for the isolation of rat Class I antigens from detergent-solubilized DA erythrocytes is described. The protocol yields a pure Class I preparation as assessed by silver staining of sodium dodecyl sulfate-polyacrylamide gels and comparison of the amino acid composition with that previously determined for H-2K/D. The antigen preparation is capable of specifically blocking the hemagglutination of DA erythrocytes by Class I-specific alloantiserum.