T-helper cell

n.
  1. Immune system cells that produce lymphokines that regulate the activities of other immune system cells, such as T cells, B cells, and monocytes, that are necessary for the differentiating of B cells into antibody-producing cells, and that often decrease in concentration following HIV infection.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.