No abstract

We report the regional mapping of human chromosome 19 genes for three apolipoproteins and a lipoprotein receptor as well as genes for three other markers. The regional mapping was made possible by the use of a reciprocal whole-arm translocation between the long arm of chromosome 19 and the short arm of chromosome 1. Examination of three separate somatic cell hybrids containing the long arm but not the short arm of chromosome 19 indicated that the genes for apolipoproteins CI, CII, and E (APOCI, APOC2, and APOE, respectively) and glucose-6-phosphate isomerase (GPI) reside on the long arm, whereas genes for the low density lipoprotein receptor (LDLR), complement component 3 (C3), and peptidase D (PEPD) reside on the short arm. When taken together with previous studies, our results suggest the following physical gene map: pter-LDLR-C3-pl3.2-PEPD-centromere-(APOE, APOCI, APOC2, GPI)-qter. In addition, we have isolated a single A phage carrying both APOCI and part ofAPOE. These genes are tandemly oriented and are separated by about 6 kilobases of genomic DNA. Since previous family studies indicate tight linkage of APOE and APOC2, the apolipoprotein genes APOCI, APOC2, and APOE form a tight complex on the long arm of chromosome 19, suggesting the possibility of coordinate regulation.

A pericentric inversion of a human X chromosome and a recombinant X chromosome [rec(X)] derived from crossing-over within the inversion was identified in a family. The rec(X) had a duplication of the segment Xq26.3--Xqter and a deletion of Xp22.3-,Xpter and was interpreted to be Xqter--Xq26.3::Xp22.3--Xqter. To characterize the rec(X) chromosome, dosage blots were done on genomic DNA from carriers of this rearranged X chromosome using a number of X chromosome probes. Results showed that anonymous sequences from the distal end of the long arm to which probes 4D8, Hx12OA, DX13, and St14 bind as well as the locus for glucose-6-phosphate dehydrogenase (G6PD) were duplicated on the rec(X). Mouse-human cell hybrids were constructed that retained the rec(X) in the active or inactive state. Analyses of these hybrid clones for markers from the distal short arm of the X chromosome showed that the rec(X) retained the loci for steroid sulfatase (STS) and the cell surface antigen 12E7 (MIC2); but not the pseudoautosomal sequence 113D. These molecular studies confirm that the rec(X) is a duplication-deficiency chromosome as expected. In the inactive state in cell hybrids, STS and MIC2 (which usually escape X chromosome inactivation) were expressed from the ree(X), whereas G6PD was not. Therefore, in the rec(X) X chromosome inactivation has spread through STS and MIC2 leaving these loci unaffected and has inactivated G6PD in the absence of an inactivation center in the q26.3--qter region of the human X chromosome. The mechanism of spreading of inactivation appears to operate in a sequence.specific fashion. Alternatively, STS and MIC2 may have undergone inactivation initially but could not be maintained in an inactive state.

The use of immunoisolation devices may allow transplantation without need for immunosuppression and could widen the indications for cell transplantation. In this study, we evaluated the survival of encapsulated parathyroid tissue in nonimmunosuppressed humans. Autologous parathyroid implants: Seven patients undergoing parathyroidectomy had devices containing small pieces of their own parathyroid tissue implanted SC. These devices were explanted after 2-4 weeks for histological evaluation. Allogeneic parathyroid implants: Four patients with chronic hypoparathyroidism were transplanted with one to three large (40 µl) and one small (4.5 µl) device filled with meshed parathyroid tissue and implanted SC. The small devices were explanted at 4 weeks, while the large ones were explanted 8.5 to 14 months after implantation. In both studies, control implants were placed in nude mice. Autologous study results: At explantation, the grafts consisted of 22 ± 6% endocrine tissue and 63 ± 7% fibrosis, while 15 ± 5% of the grafts were necrotic. Allogeneic study results: In devices explanted from the patients at 4 weeks, fibrosis dominated and only 1%, 5%, and 23% of the grafts consisted of endocrine tissue. A similar histological appearance was found in grafts from nude mice. In devices explanted at 8.5-14 months, histologically intact endocrine tissue was found in all patients. However, nearly all the tissue consisted of fibrosis. There was no detectable increase in the parathormone (PTH) level in all patients. Macroencapsulated human allogeneic parathyroid tissue can survive up to 1 year after transplantation into nonimmunosuppressed patients. However, marked fibroblast overgrowth occurred, especially in the allogeneic implant study, using meshed parathyroid tissue. This was probably not related to the allo-response, because similar findings were observed in the nude mouse implants. In future studies, better tissue preparation and improvements in the physiological milieu inside the device may help to reduce fibroblast overgrowth and increase survival of the parathyroid cells.

The generation of effector cytotoxic T lymphocytes from resting precursors proceeds through a series of steps in a pathway that, in aggregate, involves both proliferation and development of cytotoxicity. To understand the relationship of the various signals (mitogens and/or lymphokines) that bring about progress along this pathway, it is desirable to define a series of 'minimal signals', each of which stimulates the cell to proceed to a further stage in this process of differentiation. Stimulation of lymphocytes with two different monoclonal antibodies directed against the CD2 surface molecule induces a proliferative response; we report here that both CD4+ and CD8+ cells proliferate in response to such a stimulus but do not develop cytotoxicity. Addition of recombinant gamma-interferon (rIFN-gamma) or recombinant IL-2 (rIL-2) to the activated cells leads to acquisition of cytotoxic status by the CD8+ cells but not the CD4+ cells. The availability, in addition to precursors and effectors, of an apparently intermediate stage in the form of proliferating CD8+ cells that are non-cytotoxic should facilitate both cellular and molecular studies of this maturation pathway; the differences between CD4+ and CD8+ cells in development of cytotoxicity under these experimental conditions is a valuable model for understanding differentiation of T lymphocytes.