ANATOMY

Detailed explanation-1: -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-2: -Helper T cells become activated through a multistep process, which begins with antigen-presenting cells, such as macrophages. These cells ingest an infectious agent or foreign particle, partially degrade it, and export fragments of it-i.e., antigens-to the cell surface.

Detailed explanation-3: -After binding to the antigen and MHC class II molecule presented by the dendritic cell, the naïve helper T cell becomes activated and proliferates. Instead of gaining the ability to kill infected cells, helper T cells acquire the ability to activate cells that bear MHC class II molecules.

Detailed explanation-4: -Once engulfed, cellular enzymes inside the macrophage destroy the ingested particle. Some macrophages act as scavengers, removing dead or necrotic cells while others provide host immunity by engulfing microbes.