IMMUNOLOGY

Detailed explanation-1: -Another function of macrophages is to alert the immune system to microbial invasion. After ingesting a microbe, a macrophage presents a protein on its cell surface called an antigen, which signals the presence of the antigen to a corresponding T helper cell.

Detailed explanation-2: -Macrophages interact with T cells in order to bring about T cell activation in target organs, and are themselves activated by inflammatory messenger molecules (cytokines) produced by the T cells. Macrophages produce toxic chemicals, such as nitric oxide, that can kill surrounding cells.

Detailed explanation-3: -Once activated, the effector helper T cell can then activate a B cell that specifically displays the same complex of foreign peptide and class II MHC protein on its surface (see Figure 24-66).

Detailed explanation-4: -Just as with CTLs, the TCR of each helper T cell recognizes a different antigen, so only the T cell with the corresponding TCR will recognize each specific antigen. After binding to the antigen and MHC class II molecule presented by the dendritic cell, the naïve helper T cell becomes activated and proliferates.

Detailed explanation-5: -Helper T Cells Secrete Cytokines Once activated, helper T cells start to secrete proteins called cytokines, and these activate virtually all the other cells of the immune system. Cytokines stimulate the proliferation and differentiation of other immune cells such as T cells, macrophages, B cells, and leukocytes.

Detailed explanation-6: -The CD4 receptor and MHC class II molecules activate the helper T-cells. The helper T-cells release molecules called cytokines. Cytokines send messages to other immune cells to start an immune response.