The immune system

Phagocytes engulf pathogens through endocytosis, forming a phagosome. Lysosomes fuse with the phagosome, releasing enzymes that digest the pathogen. The digested products are then absorbed into the phagocyte's cytoplasm.

Macrophages engulf and present antigens to T-helper cells. T-helper cells activate B-lymphocytes. B-lymphocytes differentiate into plasma cells, which produce antibodies. Some B-lymphocytes and T-lymphocytes become memory cells.

Macrophages engulf pathogens via phagocytosis and then act as antigen-presenting cells (APCs). They present processed antigens on their surface, bound to MHC class II molecules, to T-helper cells, initiating the adaptive immune response.

Plasma cells are differentiated B-lymphocytes that produce and secrete large quantities of antibodies specific to the antigen that triggered the immune response. These antibodies circulate in the blood and lymph, targeting and neutralizing the pathogen.

T-helper cells recognize antigens presented by antigen-presenting cells (APCs) like macrophages. Once activated, they release cytokines that stimulate B-lymphocytes to differentiate and produce antibodies, and also activate T-killer cells.

T-killer cells (also known as cytotoxic T cells) recognize and kill infected or cancerous cells by binding to antigens presented on the cell surface via MHC class I molecules. They release cytotoxic substances like perforin, which creates pores in the target cell membrane, leading to cell lysis.

Memory cells are long-lived B and T lymphocytes produced during the primary immune response. Upon subsequent exposure to the same antigen, memory cells rapidly differentiate into plasma cells (B memory cells) and T-killer cells (T memory cells), resulting in a faster and stronger immune response than the primary response.

Memory cells persist in the body for a long time after the primary infection is cleared. They provide immunological memory, enabling a rapid and effective secondary immune response upon re-exposure to the same antigen, thus conferring long-term immunity to that specific pathogen.