TGF-β type II receptor–deficient thymocytes develop normally but demonstrate increased CD8+ proliferation in vivo

Abstract

We have taken advantage of the Cre/lox system to generate a mouse model with inducible deficiency of transforming growth factor ␤ receptor II (T␤RII). Using this approach, transforming growth factor ␤ (TGF-␤) signaling deficiency can be restricted to the hematopoietic system by bone marrow transplantation. Mice that received transplants with T␤RII ؊/؊ bone marrow develop a lethal inflammatory disorder closely resembling that of TGF-␤1-null mice. Previous in vitro studies have suggested multiple roles for TGF-␤ in T-cell development, including proliferation, apoptosis, and differentiation. We used our transplantation model to ask whether T-cell development is normal in the absence of TGF-␤ signaling. The findings show for the first time in vivo and in fetal thymus organ culture (FTOC) that TGF-␤ is not required for thymocytes to differentiate along the entire pathway of thymic T-cell development, as defined by the expression patterns of CD4, CD8, CD25, and CD44. In contrast to previous investigations, no increase of thymocyte apoptosis was observed. However, T␤RII-deficient CD8 ؉ thymocytes displayed a 2-fold increase in proliferation rate, as determined by bromodeoxyuridine ( IntroductionTransforming growth factor ␤ (TGF-␤) is a group of growth factor isoforms (TGF␤1, TGF␤2, and TGF␤3) involved in a multitude of physiologic functions including the immune system. They primarily interact with the TGF-␤ type I receptor (T␤RI) and type II receptor (T␤RII), both essential for propagation of the intracellular signal, including phosphorylation of Smad (small mother against decapentaplegic) proteins regulating transcriptional activation. The development of immature thymocytes to CD4 ϩ or CD8 ϩ singlepositive (SP) T cells is defined by their sequential expression of cell surface markers such as CD3, CD4, CD8, CD25, CD44, and the T-cell receptor (TCR). 1,2 Involvement of TGF-␤ in T-cell function has been suggested by in vitro studies demonstrating that TGF-␤ inhibits interleukin-1 (IL-1)-, IL-2-, and IL-7-dependent thymocyte proliferation. [3][4][5][6] Expansion of thymocytes may also be indirectly promoted by an inhibitory action of TGF-␤ on apoptosis. [7][8][9] Inhibitory effect of TGF-␤ on thymocyte development has been shown in fetal thymus organ culture (FTOC). 10 This study demonstrated that TGF-␤ causes a very early block in development within the CD4 Ϫ CD8 Ϫ population, affecting differentiation of the CD44 ϩ CD25 Ϫ into the CD44 ϩ CD25 ϩ subset of thymocytes. Further evidence for an inhibitory mode of action on T-cell development derives from the observation that TGF-␤ inhibits differentiation of CD4 ϩ thymocytes into the T helper 1 (Th1) and Th2 subsets of T helper cells. 11,12 A more complex immunoregulatory role of TGF-␤ emerged by the finding that TGF-␤ may also have stimulatory effects on immune functions. Thus, at certain stages of T-cell development, TGF-␤ stimulates, rather than inhibits, proliferation. 13 A critical role of TGF-␤ in T-cell homeostasis and function has been reinforced by studies using kn...

Normal erythropoiesis but severe polyposis and bleeding anemia in Smad4-deficient mice

“…29 TGF-␤ receptor II (TBRII) dominant-negative approaches led to autoimmune inflammatory disease and spontaneous T-cell activation. 30 Mice with TBRII deletion in bone marrow not only showed increased CD8 ϩ proliferation in vivo but also developed a lethal inflammatory disease, 18,31 and the TBRII-deficient cells of hematopoietic origin, most likely T cells, could induce multifocal inflammatory disease in a dominant way. On the contrary, our Smad4 ⌬/⌬ bone marrow recipients and VavCre;Smad4 fl/fl mice were healthy and did not show any signs of inflammatory disease.…”

“…17 The Mx-Cre-inducible mouse was widely used in studies of hematopoiesis and showed high efficiency of recombination in bone marrow. 17,18 Upon induction of Mx-Cre expression, the conditional Smad4 fl/fl alleles (fl/fl) recombined to yield dysfunctional Smad4 alleles (⌬/⌬) and these mice developed severe anemia by 6 to 8 weeks after induction. To inactivate the Smad4 fl/fl conditional allele in hematopoietic cells only, we crossed the Smad4 mice to the VavCre strain, which expresses Cre selectively in hematopoietic cells under the control of the Vav promoter.…”

Negative regulators in homeostasis of naïve peripheral T cells

“…Efforts to study the effects of TGF-β signaling on T cells have hence generated mouse models with a spectrum of phenotypes. Generally, TGF-β-mediated signals are dispensable for thymic development (90)(91)(92)(93), whereas conditional deletion of TGF-β RII on T cells results in wasting disease and death by 3-5 weeks of age (91,93).…”

Ratio of mutant JAK2-V617F to wild-type Jak2 determines the MPD phenotypes in transgenic mice

“…The MxCre inducible mouse has been widely used in studies of hematopoiesis and showed high efficiency of recombination in bone marrow. 21,22 The genetic background of the Mx-Cre and VavCre mice was determined by SNP array analysis containing 748 informative SNPs and found to be more than 97% and more than 82% C57BL/6, respectively (data not shown). Analysis of blood from double transgenic VavCre;FF1 and MxCre; FF1 mice is shown in Figure 2 and Table S1 (available on the Blood website; see the Supplemental Materials link at the top of the online article).…”