Abstract
The very late antigen complexes VLA-1 and VLA-2 which appear on long-term activated human T cells have been characterized with respect to 1) subunit arrangement, 2) location of monoclonal antibody (MAb) binding sites, 3) carbohydrate content, and 4) protein homology. Cross-linking experiments showed that the VLA-1 complex is a heterodimer composed of an Mr 210,000 subunit (alpha 1) in acid-labile association with an Mr 130,000 subunit (beta). The VLA-2 complex is a heterodimer with an Mr 165,000 subunit (alpha 2) in base-labile association with the Mr 130,000 beta subunit. The subunits of VLA-1 (alpha 1 beta) and VLA-2 (alpha 2 beta) each appear to be arranged with 1:1 stoichiometry. The MAb A-1A5 has been shown to bind to an epitope on the common beta subunit, consistent with its recognition of both the VLA-1 and VLA-2 heterodimers. On the other hand, MAb TS2/7 bound to an epitope of the alpha 1 subunit, thus explaining the specific recognition of the VLA-1 heterodimer by TS2/7. Digestion of the alpha 1, alpha 2, and beta subunits with neuraminidase and with endoglycosidase F revealed that each subunit contains substantial sialic acid and N-linked carbohydrate. By one-dimensional peptide mapping, the alpha 1, alpha 2, and beta subunits were shown to be highly nonhomologous with respect to each other, although each subunit from different T cell sources appeared highly homologous if not identical.
Highlights
The very late antigen complexesVLA-1 and VLA-2 Ta, [20]
Digestion of thea’,a’, Both VLA-1 and VLA-2 could be simultaneously immunopreand @ subunits with neuraminidase andwith endogly- cipitated by MAb A-1A5, these two structures do cosidaseF revealed that each subunit contains substnaont- always appear together [23,24,26]
To directly analyze the stoichiometry and subunit arrangements of VLA-1 and VLA-2, cross-linking experiments were carried out (Fig. 1).When both VLA-1 and VLA-2 were simultaneously immunoprecipitated by MAb A-lA5 after cross-linking with 6 pg/ml DSP two multimers were observed at M, approximately 310,000 and 255,000(Fig. 1B)
Summary
From the Dana-Farber Cancer Institute, Harvard Medical School, Boston,Massachusetts 02115. Thesubunitsof VLA-1 (CY’@ and) VLA-2 (a2@)each appeartobearranged with 1:l stoichiometry.The body (MAb) TS2/7 [24] has been described This M, 210,000/ 130,000 complex appears to be T lineage restricted among hematopoietic cells, and, its appearance defines a novel “very late” stage of activated T cell differentiation, 2 or more weeks after T cell stimulation. The suggestion that VLA-1 defines a late stage of T cell activation in vitro [23, 24] may be consistent with the appearance of VLA-1 on MAb A-1A5 has been shown to bind to an epitope on the common @ subunit, consistentwith its recognition analogous “late stage” chronic or long-term activated T cells in uiuo, such as from patients with multiple sclerosis [25]. Additional cell surface structures which appear in greatly increased amounts within a few days after T cell activation include P28 [16], GP 26 [17], T305 [18],MALA-1 [19], and
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