α2HS glycoprotein is chemotactic for mononuclear phagocytes

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Abstract
α2HS glycoprotein is a normal constituent of plasma. It has a high affinity for hydroxyapatite and is concentrated in bone 100-fold greater than albumin, however its biological function in bone is not known. We have purified α2HS from human plasma and examined it for evidence of chemotactic activity against human peripheral mononuclear cells, polymorphonuclear leucocytes and lymphocytes in Boyden chamber assays. We observed that the protein was chemotactic for mononuclear cells and that maximal cell migration occured when its concentration in the lower compartment of Boyden chambers was 10−10 M. Chemotaxis did not occur in the absence of a concentration gradient. In addition, cell migration was blocked when the cells were preincubated with 10−10 M α2HS or when the protein was preincubated with rabbit anti-human α2HS glycoprotein lgG. Neither polymorphonuclear leucocytes, which are responsive to a wide range of chemoattractants, or peripheral lymphocytes exhibited directed migration to α2HS in Boyden chamber assays. The glycoprotein appears therefore to act as a chemotaxin directed to monocyte recruitment, and we speculate that the protein may have an important role in monocyte recruitment to bone and possibly their subsequent fusion and differentiation into functional osteoclasts.
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