We investigated intraepithelial T cells from the small intestine, SI (jejunum, ileum) and the large intestine, LI (colon) of euthymic (BALB/c, H-2d; C.B-17+/+, H-2d; C57BL/6, H-2b) and athymic (C57BL/6 nu/nu; BNX bg/bg nu/nu xid/xid) mice. From individual euthymic and athymic mice, 7 x 10(6) intraepithelial lymphocytes (IEL) per mouse were isolated from the SI. Ten-fold lower numbers of IEL were obtained from the LI epithelium (4 x 10(5) IEL per mouse). Thymus-dependent and -independent T cells represented > 80% of SI-IEL but the fraction of T cells was reduced from 20% to 40% in LI-IEL. In euthymic mice, alpha beta T cells predominated in SI-IEL and in particular in LI-IEL populations, while SI-IEL and LI-IEL populations of athymic mice contained predominantly gamma delta T cells. The intraepithelial T cell subset distribution was different in SI versus LI: mainly CD8+ T cells were present in the SI, but a large CD4+ T cell subset was present in the LI. 'Double positive' CD4+ CD8 alpha+ T cells were present mainly in the SI epithelium but were rare in the LI epithelium. In euthymic as well as athymic mice, T cells expressing the homodimeric CD8 alpha alpha isoform predominated in the SI epithelium, while T cells expressing the heterodimeric CD8 alpha beta isoform predominated in the LI epithelium. LI-derived TCR alpha beta+ IEL displayed the CD2+ CD28+ LPAM-1/2- M290+ phenotype, and a fraction of them expressed the L-selectin LECAM-1. In contrast, a large fraction of TCR alpha beta+ SI-IEL was CD2- CD28- LPAM-1/2- M290+ and LECAM-1-. RAG-1/2 expression was detectable by RT-PCR in IEL from the SI but not the LI. Striking differences in phenotype were thus apparent between thymus-dependent and thymus-independent T cells in the epithelial layer of the jejunum/ileum and the colon of the mouse.

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Intravenous injection of nonfractionated BALB/c-H-2dm2 (dm2) (Ld-) spleen cells into 4-week-old, semi-allogeneic (H-2d, Ld+) C.B-17 scid/scid severe combined immunodeficient (scid) mice (2 x 10(7) cells/mouse) reconstituted T lymphopoiesis in thymi and repopulated the lymphoid white pulp in spleens of these immunodeficient recipients. Transplantation of dm2 thymocytes into young scid mice (5 x 10(7) cells/mouse) established a donor-derived CD3+ T cell population in spleens of recipient scid mice, in which CD4+T cells predominated. This was demonstrated by marker analyses of thymocytes and splenocytes, and determinations of serum immunoglobulin levels in transplanted scid mice. Transfer of splenocytes from young primary scid recipients into young secondary or tertiary recipients (3 x 10(6) cells/mouse) engrafted preferentially dm2-derived CD3+CD4+CD8- T cells in spleens of scid mice despite the strong selective Ld-associated alloantigenic stimulus for CD8+ T cells. Intravenous injections of nonfractionated dm2 spleen cells (2 x 10(7) cells/mouse) or thymocytes 5 x 10(7) cells/mouse) into 10- to 12-month-old, "leaky" scid mice induced severe clinical signs of graft-vs.-host disease (GVHD) in all scid recipients. Lymphoid repopulation of spleen and thymus in old scid recipients was incomplete. This GVHD was not transferrable by injecting 3 x 10(6) spleen cells from old diseased primary scid recipients into secondary or tertiary young scid recipient mice. In these serial transfers, dm2-derived CD3+CD4+CD8- T cells were again preferentially engrafted in spleens of scid recipients. Transfer of purified CD4+ dm2 T cells into young scid mice (2 x 10(5) to 5 x 10(5) cells/mouse) engrafted this T cell subset into the spleen of semi-allogeneic scid recipients. This was revealed by histological examinations, surface marker analyses, in vitro isolation of donor-type CD3+CD4+ T cell lines from spleens of transplanted scid mice, and serial transfer experiments. These data indicated that the CD4+ T cell compartment of scid mice can be selectively repopulated by semi-allogeneic T cells. Injections of purified CD8+ dm2 T-cells into young scid mice (2 x 10(5) cells/mouse) did not establish a CD8+ T cell graft in spleens of recipients. It was necessary to inject transplanted scid mice biweekly with 10(4) units recombinant interleukin 2 to establish and/or maintain transferred dm2 CD8+ T cells in spleens of these recipients, dm2 CD8+ T cell-transplanted and interleukin 2-treated scid mice did not develop any evidence of GVHD over the 9-week observation period.

Young (less than 3 months of age) and old (greater than 1 year of age) C.B-17 scid/scid mice were tested for the presence of immunoglobulin in serum and CD3+ T cells in spleen and peritoneal cavity. In all old severe combined immune deficiency (scid) mice tested we found detectable, but very variable levels of serum immunoglobulin as well as splenic and peritoneal CD3+ T cells comprising 3% to 10% of the nonfractionated cell populations of these organs (n = 10). In contrast, none of the analyzed young scid mice showed any evidence of peripheral lymphocytes. Low numbers (2 x 10(5) to 5 x 10(5) cells/mouse) of highly purified CD4+ cells from congenic C.B-17 or BALB/c donor mice were injected intravenously into young scid recipient mice. A CD4+ T cell population was clearly engrafted when transplanted scid mice were analyzed 8 to 13 weeks after T cell transfer: (a) a CD3+CD4+CD8- T cell population was detectable in the spleens of all recipient scid mice by flow microfluorometry analyses; (b) CD3+CD4+CD8 T cell lines could be grown out of these spleens in vitro; (c) the histological examination revealed evidence of lymphoid cell repopulation in the spleens of all transplanted scid mice and (d) transplanted CD4+ T cell populations could be serially transferred into secondary and tertiary recipient scid mice. These data indicate that scid mice can be constructed in which only the CD4+ T cell compartment is selectively reconstituted. In contrast to the successful engraftment of CD4+ T cell, highly purified congenic CD8+ T cells could not be engrafted into the spleen of scid mice.

We studied the peripheral T cell compartment of H-2b severe combined immunodeficient (scid) mice that express a transgenic (tg) alpha beta T cell receptor (TcR) specific for the H-Y (male) epitope presented by the H-2 class I Db molecule. Large populations of CD3+ NK1.1-TCR beta T+ T cells were present in spleen, mesenteric lymph nodes, peritoneal cavity, lamina propria and epithelial layer of the small and large intestine of 6- to 10-month-old, male and female tg scid mice. Only low numbers of CD3+ T cells were recovered from inguinal, popliteal, or axillary lymph nodes. We studied CD4+ T cells in these tg scid mice. CD4+ T cells were found in the peritoneal cavity, in the mesenteric lymph nodes and in the intraepithelial layer and lamina propria of the gut. All CD4+ T cells were CD44+ (i.e. showed evidence of antigen-driven differentiation) and expressed the tg V beta 8.2 TcR beta-chain (TcR beta T+). Only few CD4+ T cells expressed the tg V alpha 3+ TcR alpha-chain (TcR alpha T). cDNA was prepared from CD4+ T cells from spleen or mesenteric lymph nodes of individual male and female tg scid mice; sequence analyses of polymerase chain reaction-amplified, endogenous TcR alpha-chain (TcR alpha E) transcripts indicated that > 90% of the TcR alpha E-chain transcripts were in-frame, that the TcR alpha E repertoire in CD4+ T cell populations was oligoclonal, and that the TcR alpha E repertoire was different in individual tg scid mice. Hence, an oligoclonal, leaky CD4+ T cell population is selected in tg scid mice that apparently responds to gut-derived antigens. No inflammatory bowel disease (IBD) was evident in the small or large intestine of 6- to 10-month old tg scid mice. After adoptive transfer of purified CD4+ T cells (10(5) cells per mouse) from tg scid mice into non-tg H-2b scid mice, CD4+ TcR alpha T-beta T+ cells were found in gut tissues of the immunodeficient host. Transplanted scid mice developed clinical and histological signs of IBD. An oligoclonal, gut-homing, memory/effector CD4+ CD44+ TcR beta T+ TcR alpha T-T cell subset from leaky tg scid mice thus has a pathogenic potential when released from the control of TcR beta T+ TcR alpha T+ T cells.