MadSci Network: Immunology

Re: Why does PHA (phytohaemagglutanin) stimulate T cells to divide?

Date: Wed May 5 17:17:38 1999
Posted By: Jeffrey Dorfman, Post-doc/Fellow, immunology, national Institutes of Health
Area of science: Immunology
ID: 925900443.Im

PHA is a member of a family of proteins called lectins that bind to sugars. Different lectins have specificities for different sugars; some, like PHA bind to paricular sugar modifications of cell surface proteins.

PHA is able to crosslink a glycosylated (sugar modified) protein or proteins on the surface of T cells.

I spent some time doing some medline searches and asking some colleagues. To the best of my ability to find, neither the particular sugar structure bound by PHA or the identity of the protein target(s) that have this modification on T cells are known. It could be a protein or proteins associated with the TCR/CD3 complex.

Antigen presenting cells (eg macrophages) must be present for PHA to be able to stimulate T cells. This may be because costimulatory signals must be received by the T cells (eg B7/CD28) or because the PHA may bind to the T cell but the antigen presenting cells is necessary to properly crosslink it or both. Again, I don't know if that is known; in any event, I don't know.

Jeff Dorfman

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