<s>[INST] context: In a tuberculin skin test, T cell proliferation is increased by secretion of interleukins. An extract of tuberculin (an antigen of lipoprotein composition obtained from the tubercle bacillus) is injected into the skin of a person who has had tuberculosis or has been immunized against tuberculosis. Merriory helper T cells react to the tuberculin and secrete Il-2, which up regulates Il-2 receptors. Il-2 binding to Il-2 receptors on the same cell is an example of autocrine regulation in which a cell secretes a ligand for a receptor on its own surface. The result of this up regulation and ligand receptor binding is an increase in T cell proliferation. T cell derived cytokines such as tumor necrosis factor-alpha and beta (TN Fα and β) induce leukocyte recruitment. Production of gamma-(γ)-interferon by helper T cells attracts and activates macrophages (monocytes comprise most of the cellular infiltrate). γ -Interferon also converts other cells (such asendothelial cells) to antigen-presenting cells by induction of class II MHC expression, which further augments the response. The result of the activity of helper T cells is a dramatic increase in the number of lymphocytes and macrophages at the test site, which produces swelling. IL-I is synthesized by antigen-presenting cells and macro phages with helper T cells as the targets. [/INST] question: In a positive tuberculin skin test, helper T cells assist in which of the following ways? | options: A: Autocrine-mediated inhibition of proliferation of helper T cells B: The down regulation of IL-2 receptors on helper T cells C: Secretion of interleukins that promote T cell proliferation D: Secretion of IL-I | answer: C </s>