Fibronectin promotes proliferation of naive and memory T cells by signaling through both the VLA-4 and VLA-5 integrin molecules.
The capacity of purified fibronectin to costimulate human T cell DNA synthesis was examined. Low concentrations of immobilized fibronectin, but not soluble fibronectin, augmented anti-CD3-induced proliferation of highly purified human T cells. In the absence of anti-CD3 stimulation, immobilized fibronectin did not induce T cell proliferation alone or in the presence of IL-2 or phorbol dibutyrate. Although fibronectin is present in high concentrations in the serum, immobilized fibronectin was able to costimulate T cell proliferation when cells were cultured in serum-containing medium. Immobilized collagen type I did not enhance anti-CD3 stimulated T cell responses, whereas gelatin (denatured collagen) and laminin were able to enhance anti-CD3 stimulated T cell responses modestly. The effects of gelatin, however, appeared to be indirect, because it could not enhance responses in medium devoid of fibronectin. Immobilized fibronectin enhanced anti-CD3 induced proliferation of both CD45RA dim and CD45RA bright subsets within both the CD4+ and CD8+ subpopulations of T cells, although cells with the CD45RA dim phenotype were costimulated by lower concentrations of immobilized fibronectin. Enhancement of anti-CD3 induced proliferation by immobilized fibronectin was completely inhibited by a mAb to CD29, the integrin beta 1-chain (4B4) and not by a variety of other mAb. In contrast to its effects on proliferation, 4B4 only partially blocked T cell binding to anti-CD3 and fibronectin-coated macrowells. These findings suggested that the interaction between fibronectin and its receptor transduced a signal to the T cell and did not merely stabilize the interaction between anti-CD3 and the CD3 complex. Further experiments confirmed this observation. Thus fibronectin could enhance anti-CD3 responses when it was immobilized to a separate surface. The augmentation of anti-CD3 stimulated proliferation induced by immobilized fibronectin was also inhibited partially by mAb to either VLA-4 or VLA-5 and completely by a combination of the two mAb. The mAb to VLA-4 not only blocked the capacity of immobilized fibronectin to enhance anti-CD3-induced T cell proliferation but also directly costimulated T cell responses. Thus, at least two fibronectin receptors are involved in fibronectin-mediated costimulation of T cell proliferation. These studies indicate that signals are transduced through the fibronectin receptors, VLA-4 and VLA-5, that augment T cell responses and therefore implicate the extracellular matrix protein fibronectin as an important influence regulating T cell responsiveness in vivo.
Harold C. Simmons Arthritis Research Center, University of Texas Southwestern Medical Center, Dallas 75235.
L S
LS
Davis
N
N
Oppenheimer-Marks
J L
JL
Bednarczyk
B W
BW
McIntyre
P E
PE
Lipsky
D000911:Antibodies, Monoclonal / Q000276:immunology; D000943:Antigens, Differentiation / Q000276:immunology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology; D017252:CD3 Complex; D005353:Fibronectins / Q000494:pharmacology*; D006801:Humans; D007156:Immunologic Memory; D019012:Integrin beta1; D016023:Integrins / Q000502:physiology*; D008213:Lymphocyte Activation / Q000187:drug effects*; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D017469:Receptors, Fibronectin; D011971:Receptors, Immunologic / Q000502:physiology; D013601:T-Lymphocytes / Q000187:drug effects* / Q000276:immunology
D000911:Antibodies, Monoclonal; D000943:Antigens, Differentiation; D000945:Antigens, Differentiation, T-Lymphocyte; D017252:CD3 Complex; D005353:Fibronectins; D019012:Integrin beta1; D016023:Integrins; D011948:Receptors, Antigen, T-Cell; D017469:Receptors, Fibronectin; D011971:Receptors, Immunologic