A novel biologic function of serum amyloid A. Induction of T lymphocyte migration and adhesion.

In the course of an inflammatory response, the concentration of serum amyloid A (SAA), a hepatocyte-derived acute phase protein, increases up to 1000-fold above the normal level. Although SAA was previously thought to be immunosuppressive, we recently reported that SAA is a potent chemoattractant for monocytes and neutrophils. The present study shows that recombinant human (rh) SAA also induces directional migration of T cells in vitro. Phenotypic analyses revealed that CD4+ and CD8+ T cell subsets were equally responsive to rhSAA, whereas CD45RA cells were also not selectively attracted by rhSAA. The T cell chemotaxis induced by rhSAA was inhibited by pretreatment of cells with pertussis toxin, suggesting the interaction of rhSAA with a G-protein-coupled receptor species. T cells pretreated with an optimal concentration of SAA exhibited enhanced adherence to human umbilical cord endothelial cell monolayers. Subcutaneous administration of rhSAA into huPBL-SCID mice caused the infiltration of human T lymphocytes at the injection sites by 4 h. These results suggest that SAA may play an important role in recruiting T lymphocytes, as well as neutrophils and monocytes into inflammatory lesions.