Levels of Art2+ cells but not soluble Art2 protein correlate with expression of autoimmune diabetes in the BB rat.

ART2a and ART2b are isoenzymes expressed on the surface of mature T cells and intraepithelial lymphocytes (IELs) in the rat. They exhibit both adenosine diphosphoribosyltransferase and nicotine adenine dinucleotide (NAD) glycohydrolase activities, and both can generate a transmembrane signal that modulates T cell activation. The presence or absence of ART2+ T cells modulates the expression of autoimmune diabetes in the BB rat. ART2 also circulates in a soluble form whose function is unknown. We tested the hypothesis that circulating ART2 protein regulates the expression of autoimmunity. We compared the kinetics, regulation, and source of soluble ART2 in normal rats and in rats with autoimmune diabetes. Basal levels of soluble ART2 varied greatly among strains of rats and were lowest in the diabetes-prone BB (BBDP/Wor) rat. In diabetes-resistant BB (BBDR/Wor) rats, administration of anti-ART2a antibody, which is known to induce diabetes, resulted in transient clearing of soluble ART2a that was followed rapidly by a rebound increase. Repeated treatment of BBDR/Wor rats with anti-ART2a antibody resulted in sustained supraphysiologic levels of soluble ART2a. Although the number of peripheral ART2a+ T cells is known to correlate with the expression of diabetes in BBDR/Wor rats, the level of soluble ART2a protein did not. The source of the soluble ART2 protein in the rat appeared to be the gut. The results suggest that ART2+ T cells and soluble ART2 protein may subserve different immunomodulatory functions.

NOD/LtSz-Rag1null mice: an immunodeficient and radioresistant model for engraftment of human hematolymphoid cells, HIV infection, and adoptive transfer of NOD mouse diabetogenic T cells.

Development of a small animal model for the in vivo study of human immunity and infectious disease remains an important goal, particularly for investigations of HIV vaccine development. NOD/Lt mice homozygous for the severe combined immunodeficiency (Prkdcscid) mutation readily support engraftment with high levels of human hematolymphoid cells. However, NOD/LtSz-scid mice are highly radiosensitive, have short life spans, and a small number develop functional lymphocytes with age. To overcome these limitations, we have backcrossed the null allele of the recombination-activating gene (Rag1) for 10 generations onto the NOD/LtSz strain background. Mice deficient in RAG1 activity are unable to initiate V(D)J recombination in Ig and TCR genes and lack functional T and B lymphocytes. NOD/LtSz-Rag1null mice have an increased mean life span compared with NOD/LtSz-scid mice due to a later onset of lymphoma development, are radioresistant, and lack serum Ig throughout life. NOD/LtSz-Rag1null mice were devoid of mature T or B cells. Cytotoxic assays demonstrated low NK cell activity. NOD/LtSz-Rag1null mice supported high levels of engraftment with human lymphoid cells and human hemopoietic stem cells. The engrafted human T cells were readily infected with HIV. Finally, NOD/LtSz-Rag1null recipients of adoptively transferred spleen cells from diabetic NOD/Lt+/+ mice rapidly developed diabetes. These data demonstrate the advantages of NOD/LtSz-Rag1null mice as a radiation and lymphoma-resistant model for long-term analyses of engrafted human hematolymphoid cells or diabetogenic NOD lymphoid cells.

Enhanced human CD4+ T cell engraftment in beta2-microglobulin-deficient NOD-scid mice.

Genetic crosses produced NOD/LtSz mice doubly homozygous for the severe combined immunodeficiency (scid) mutation and the beta2m (B2m) null allele. Both NOD/LtSz-scid/scid and NOD/LtSz-scid/scid B2m(null) mice lacked mature lymphocytes and serum Ig. However, homozygosity for the B2m(null) allele also resulted in the absence of MHC class I expression, loss of NK cell activity, accumulation of iron in the liver, and rapid clearance of human IgG1. NOD/LtSz-scid/scid B2m(null) mice supported markedly elevated levels of human T cell engraftment, compared with NOD/LtSz-scid/scid control animals, following injection with human PBMC. The increased engraftment was associated with a major increase in the number of human CD4+ T cells. Following injection with 20 million human PBMC, levels of human CD4+ T cells in the peripheral blood and spleen of NOD/ LtSz-scid/scid B2m(null) mice were 6- to 7-fold higher than those in NOD/LtSz-scid/scid mice and >50-fold higher than those in C.B-17-scid/scid mice. The resulting normalization of CD4+/CD8+ ratios in NOD/LtSz-scid/scid B2m(null) mice is in sharp contrast to that observed in NOD/LtSz-scid/scid mice or in C.B-17-scid/scid mice. Circulating human IgG was cleared 6-fold more rapidly in NOD/LtSz-scid/scid B2m(null) mice than in NOD/LtSz-scid/scid mice. This rapid IgG clearance suggested a failure of the engrafted human lymphoid cells to maintain high circulating levels of human IgG. The higher levels of human CD4+ T cells and the normalization of the CD4:CD8 ratio that are observed in human PBMC-engrafted NOD/LtSz-scid/scid B2m(null) mice suggest that this system may be an excellent model for studies of HIV pathogenesis.

Improved engraftment of human cord blood stem cells in NOD/LtSz-scid/scid mice after irradiation or multiple-day injections into unirradiated recipients.

Human lymphoematopoietic stem cells engraft in irradiated immunodeficient mice that are homozygous for the severe combined immunodeficiency (scid) mutation. Engraftment levels in C.B-17-scid/scid mice, however, have been low and transient, decreasing the utility of this model for investigation of the development potential and function of human stem cells. In the present study, we have used NOD/LtSz-scid/scid mice as recipients and human cord blood as a source of donor stem cells. Our results demonstrate that NOD/LtSz-scid/scid mice support approximately fivefold higher levels of human stem cell marrow engraftment than do C.B-17-scid/scid mice. Human CD34+ cells are present in the marrow of recipient mice, and the engrafted cells readily peripheralize to the circulation of the host. Terminal differentiation of the stem and progenitor cells into mature progeny is limited. Using a multiple-day injection protocol developed in mice, which allows engraftment of stem cells between congenic mice in the absence of irradiation preconditioning, we observed high levels of human cell engraftment in unirradiated NOD/LtSz-scid/scid recipients after three or five consecutive-day injections. These results demonstrate that NOD/LtSz-scid/scid mice support high levels of human stem cell engraftment and that xenogeneic lymphohematopoietic stem cells can engraft in unirradiated hosts without the need for ablative reconditioning. This model will be useful for the in vivo investigation of human stem cells and for the preclinical analysis of human stem cells for transplantation.

Thymus atrophy and changes in thymocyte subpopulations of BN rats with mercury-induced renal autoimmune disease.

Administration of low doses of mercury induces autoantibodies to laminin and autoimmune glomerulonephropathy in BN, MAXX and DZB rats as well as in (BN x LEW)F1 hybrids. LEW strain rats are resistant to these immunotoxic effects. Susceptible rats also show lymphoid hyperplasia in spleen and lymph nodes and severe thymic atrophy. It is still uncertain whether these mercury-induced changes have any role in the induction of autoimmune responses to laminin. In the present study, we have examined the effects of mercury on the thymus of susceptible and resistant rats. Histological analysis of thymuses from BN rats revealed extensive disorganization within 15 days following mercury treatment, with loss of demarcation between cortex and medulla. Numbers of thymus cells were significantly decreased in both BN and (BN x LEW)F1 hybrid rats injected with HgCl2. There was no apparent increase in apoptotic cells in the thymus of these animals. By flow cytometry we detected a relative and absolute loss of double-positive CD4+ CD8+ thymocytes in BN (but not in LEW rats) within 15 days of mercury treatment. There was a corresponding increase in the relative proportion of single-positive (CD4+ or CD8+) and double-negative CD4- CD8- thymocytes in mercury-treated BN rats. Absolute increases in the number of CD4+ single-positive thymocytes were also observed. In contrast, mercury-treated LEW rats had no changes in thymus architecture or significant decreases in cell numbers. Since the thymus is important in both position and negative selection of developing thymocytes, immunotoxic effects of mercury on its structure and thymocyte subpopulations may have multiple consequences. Alternatively, we suggest the hypothesis that autoimmunity (and in particular autoantibodies to laminin) may be responsible for the changes observed in the thymus.

HIV-1 infectivity of human T cells in a human/murine chimeric fetal thymic organ culture system.

Human cord blood (HuCB) can colonize a murine fetal thymus organ culture (FTOC) and generate phenotypically immature (CD4+ CD8+) and mature (CD4+ CD8-; CD4- CD8+) T cells. We have used this model system to demonstrate that the human T cells that develop in this culture system can be infected with HIV-1. A cytopathic and non-cytopathic patient isolate of HIV-1 were used to infect FTOC established using C.B-17 or NOD/LtSz.scid/scid strain fetal thymic lobes colonized with HuCB. At 13-15 days after infection, FTOC were placed in co-culture with human PHA-blasts. These co-cultures demonstrated the presence of replicating HIV-1. Few human CD45+ cells were detectable in the thymic lobes that were infected with HIV-1, while high numbers of human CD45+ T cells were present in the uninfected cultures. These results demonstrate the cytopathicity of HIV-1 on human T lymphocytes that have developed in a HuCB colonized FTOC system.