The Very Late Activation Antigen (VLA) proteins are a family of five related heterodimers, which also are part of the integrin superfamily of cell adhesion molecules. Except for the identification of VLA‐5 as a fibronectin receptor structure, the functions of the VLA proteins have remained unclarified. In this paper, immuno‐precipitation experiments with both anti‐α and anti‐β subunit antibodies showed that the previously identified cell adhesion receptor for collagen, extracellular matrix receptor II (ECMRII), is equivalent to VLA‐2. At the same time a previously described multispecific cell adhesion receptor for collagen, fibroncclin, and laminin (ECMRI) has been shown to be identical to VLA‐3. Although the mAb 12F1 and P1H5 both recognized VLA‐2 (ECMRII), they appeared to define distinct epitopes on the α2 subunit. On the other hand, the mAb PIB5 and J143 recognized the α3 subunit of VLA‐3 (ECMRI) at or near the same site. Consistent with the collagen receptor functions of VLA‐2 (ECMRII) and VLA‐3 (ECMRI), anti‐VLA β antiserum blocked cell attachment to collagen.
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