Interleukin 7 receptor-deficient mice lack gammadelta T cells

The role of Jak3 in lymphoid development, activation, and signaling

Mutations in a number of lymphoid signaling molecules lead to immunodeficiencies in mice and humans. Among these, one very pleiotropic syndrome results from deficiencies in an array of cytokine signaling pathways utilizing a cytokine receptor common gamma chain, gammac, and the tyrosine kinase Jak3. Recent advances in our understanding of the role of gammac and Jak3 in lymphocyte development and function highlight the importance of cytokine receptor signaling pathways in regulating lymphoid homeostasis and responsiveness.

Intrathymic delta selection events in gammadelta cell development

The major pathway of gammadelta cell development is shown to be regulated by in-frame rearrangements at the T cell receptor (TCR) delta locus. Such "delta selection" occurs at or around the same point in thymocyte development as selection for in-frame rearrangements at the TCRbeta locus. However, there are at least two major differences with beta selection: first, delta selection commonly involves selection on the cognate TCR chain, gamma, suggesting that there is no "preTgamma" chain of major biological significance; second, most gammadelta-selected thymocytes differentiate rather than proliferate. Nonetheless, some delta selection events seemingly facilitate thymocyte expansion, similar to alphabeta T cell development. In these cases, TCRgamma selection is less obvious. Furthermore, the capacity of individual gamma chains to facilitate gammadelta selection is shown to vary with developmental age. The results further clarify early T cell development at the beta selection/delta selection stage and place clear constraints on models of cell fate determination.

Bcl-2 rescues T lymphopoiesis, but not B or NK cell development, in common gamma chain-deficient mice

The common cytokine receptor gamma chain (gamma(c)) is an indispensable subunit for the formation of lymphoid-related cytokine receptors, including IL-7 and IL-15 receptors, that mediate nonredundant or critical signals for the differentiation of T and B cells and natural killer (NK) cells, respectively. We introduced the bcl-2 transgene driven by E mu or H-2K promoters into gamma(c)-deficient mice that lack all three lymphoid subclasses. The forced expression of Bcl-2 restored all stages of T lymphopoiesis, but not B or NK cell development, indicating that a primary function of gamma(c)-mediated signals in the T lineage might be to maintain cell survival. Therefore, the development of T, B, and NK cells may be influenced by distinct intracytoplasmic signaling cascades that are activated by coupling of gamma(c)-related receptors.

Clonal Proliferation and Cytokine Requirement of Murine Progenitors for Natural Killer Cells

We have established a clonal cell culture system that supports the proliferation of committed natural killer (NK) cell progenitors of mice to investigate the pathway and cytokine regulation of NK cell development. Day 14 fetal thymocytes cultured in methylcellulose with interleukin-7 (IL-7), IL-15, and steel factor (SF ) formed diffuse colonies that could not be classified to known colony types. Single-cell origin of the colonies was established by micromanipulation of the colony-forming cells. Cells in the colonies are very blastic, showing no cytoplasmic differentiation, and express Ly5, Thy-1, and CD25 but not myeloid, B, mature T, or NK cell markers. The cells lack T, B, and myeloid potentials but can differentiate to mature NK cells in fetal thymus organ culture, suggesting that the colonies consist of NK committed progenitors. Examination of the minimal cytokine requirement for the NK colony formation showed that IL-7 and SF are indispensable for the formation of immature NK cell colonies. Both IL-2 and IL-15 increased the frequency of colonies. In contrast to IL-2, IL-7, and IL-15, IL-4 strongly inhibited the formation of the colonies. This quantitative clonal culture will provide a useful means to examine the mechanism of NK cell development.

Defective T-cell receptor gamma gene rearrangement in interleukin-7 receptor knockout mice

T-cell receptor (TCR) genes need to be rearranged by a site specific-VDJ recombinase before they are expressed. This process, initiated in CD44+25+ thymocytes, takes place during the early stage of T-cell differentiation in the thymus. Interleukin-7 receptor alpha chain knockout (IL-7R-/-) mice are severely deficient in B-lymphocytes and alpha beta T-cells and completely lack the gamma delta T-cell lineage. Thymocyte development is arrested at a very early stage (DN CD44+CD25-). Because this arrest is earlier than in mice with a block in VDJ recombination, we examined the rearrangement status of TCR genes in thymocytes from IL-7R-/- mice. The TCR beta locus showed a nearly normal pattern of VDJ rearrangements, consistent with the presence of alpha beta T-cells in these mice. However, TCR gamma locus rearrangement was absent or severely reduced for all the V gamma genes analyzed (V gamma 3, V gamma 4, V gamma 1.1, V gamma 1.2 and V gamma 2). In contrast, the delta locus showed little reduction in rearrangement. The defect in gamma rearrangements in IL-7R-/- thymocytes is not simply due to an absence of mature gamma delta T-cells, since TCR delta-/- mice, which also have only alpha beta T-cells, had normal levels of gamma and delta rearrangements. These findings indicate that one or both of the two known ligands of IL-7R, IL-7 and thymic stromal lymphopoietin (TSLP) serves as an extrinsic signal to specifically rearrange the TCR gamma locus.

Abnormal development of intestinal intraepithelial lymphocytes and peripheral natural killer cells in mice lacking the IL-2 receptor beta chain

The interleukin-2 receptor beta chain (IL-2R beta) is expressed on a variety of hematopoietic cell types, including natural killer (NK) cells and nonconventional T lymphocyte subsets such as intestinal intraepithelial lymphocytes (IEL). However, the importance of IL-2R beta-mediated signaling in the growth and development of these cells has yet to be clearly established. We have investigated IEL and NK cells in mice deficient for IL-2R beta and describe here striking defects in the development of these cells. IL-2R beta-/- mice exhibited an abnormal IEL cell population, characterized by a dramatic reduction in T cell receptor alpha beta CD8 alpha alpha and T cell receptor gamma delta lymphocytes. This selective decrease indicates that IEL can be classified into those whose development and/or differentiation is dependent on IL-2R beta function and those for which IL-2R beta-mediated signaling is not essential. NK cell development was also found to be disrupted in IL-2R beta-deficient mice, characterized by a reduction in NK1.1+CD3- cells in the peripheral circulation and an absence of NK cytotoxic activity in vitro. The dependence of NK cells and certain subclasses of IEL cells on IL-2R beta expression points to an essential role for signaling through this receptor, presumably by IL-2 and/or IL-15, in the development of lymphocyte-subsets of extrathymic origin.

Shared gamma(c) subunit within the human interleukin-7 receptor complex. A molecular basis for the pathogenesis of X-linked severe combined immunodeficiency

Genetic evidence suggests that mutations in the gamma(c) receptor subunit cause X-linked severe combined immunodeficiency (X-SCID). The gamma(c) subunit can be employed in receptor complexes for IL-2, -4, -7, -9, and -15, and the multiple signaling defects that would result from a defective gamma(c) chain in these receptors are proposed to cause the severe phenotype of X-SCID patients. Interestingly, gene disruption of either IL-7 or the IL-7 receptor (IL-7R) alpha subunit in mice leads to immunological defects that are similar to human X-SCID. These observations suggest the functional importance of gamma(c) in the IL-7R complex. In the present study, structure/function analyses of the IL-7R complex using a chimeric receptor system demonstrated that gamma(c) is indeed critical for IL-7R function. Nonetheless, only a limited portion of the cytoplasmic domain of gamma(c) is necessary for IL-7R signal transduction. Furthermore, replacement of the gamma(c) cytoplasmic domain by a severely truncated erythropoeitin receptor does not affect measured IL-7R signaling events. These findings support a model in which gamma(c) serves primarily to activate signal transduction by the IL-7R complex, while IL-7R alpha determines specific signaling events through its association with cytoplasmic signaling molecules. Finally, these studies are consistent with the hypothesis that the molecular pathogenesis of X-SCID is due primarily to gamma(c)-mediated defects in the IL-7/IL-7R system.

The V-J recombination of T cell receptor-gamma genes is blocked in interleukin-7 receptor-deficient mice

IL-7R-deficient mice have severely impaired expansion of early lymphocytes and lack gamma delta T cells. To elucidate the role of IL-7R on gamma delta T cell development, we analyzed the rearrangements of TCR-alpha, beta, gamma, and delta genes in the thymus of the IL-7R-deficient mice. Southern blot analysis with a J gamma 1 probe revealed that more than 70% of J gamma 1 and J gamma 2 alleles are recombined to form distinct V gamma 1.2-J gamma 2 and V gamma 2-J gamma 1 fragments in control mice. On the contrary, no such recombination was detected in the mutant mice. The rearrangements in the TCR-alpha, beta, and delta loci were comparably observed in control and mutant mice. PCR analysis indicated that the V-J recombination of all the V gamma genes is severely hampered in the mutant mice. The mRNA of RAG-1, RAG-2, Ku-80, and terminal deoxynucleotidyl transferase (TdT) genes was equally detected between control and mutant thymi, suggesting that the expression of common recombination machinery is not affected. These data demonstrated that the V-J recombination of the TCR gamma genes is specifically blocked in the IL-7R-deficient mice and suggested the presence of highly specific regulation for TCR gamma gene rearrangement.

Identification of novel lymphoid tissues in murine intestinal mucosa where clusters of c-kit+ IL-7R+ Thy1+ lympho-hemopoietic progenitors develop

We have revealed that about one and a half thousand tiny clusters, filled with one thousand closely packed lymphocytes, can be found throughout the murine small and large intestinal mucosa. They are located in crypt lamina propria (cryptopatches; CP) and can be first detected at 14-17 d after birth. A large fraction of lymphocytes in CP expresses c-kit, IL-7R, Thy1 and a lymphocyte function-associated antigen, LFA-1, whereas most of them remain CD3-, TCR alpha beta-, TCR gamma delta-, sIgM-, and B220-. The population size of IL-2R alpha+, HSA+ and Pgp-1+ subsets is variable (20-50%) and the composition of CD8+, Ly-1+, and CD4+ subsets is smaller but also variable (3-20%). In the small intestine, CP do not contain cells undergoing apoptosis nor cells bearing RAG-1 molecules, but do contain dendritic stromal cells bearing CD11c/CD18 molecules. The frequency of DNA replicating cells in CP is higher than that in Peyer's patches (PP), is lower than that in the thymic cortex and is almost comparable with that in the thymic medulla. The numbers of CP remain the same in aged mice (> 114 wk) but double after estrogen treatment even though the thymi are attenuated sharply in both conditions. Thus, with respect to histogenesis, lymphocyte composition and tissue level of cellular behavior, neither PP, isolated lymphoid follicles, peripheral LNs, nor thymus are identical with CP. Finally, CP are virtually absent in lamina propria of IL-7R-deficient mice that display a profound reduction in thymic and peripheral lymphoid cellularity. By contrast, CP are present in germ-free mice and in athymic (nu/nu), SCID, TCR beta x delta-/-, RAG-2-/-, PP-deficient (aly/aly), stem cell factor (Sl/Sld) and c-kit (W/Wv) mutant mice. Taking all of these results together, CP are the first identification of gut-associated murine lymphoid tissues where the generation of IL-7-dependent lympho-hematopoietic progenitors for T and/or B cell descendants may start to take place at the age of commencement of weaning.