Basic Overview

Physical barriers such as skin, tears, and saliva that prevent pathogens from entering the body.

Substances like anti-microbial peptides and low pH in the gut that inhibit the growth of pathogens.

Normal bacteria that compete with harmful bacteria for resources and space, preventing their overgrowth.

Immune cells that reside in tissues, trigger inflammation as an alarm response, and engulf and destroy pathogens through phagocytosis.

Immune cells that circulate in the bloodstream, wait for the alarm signal from macrophages, and engulf and destroy pathogens through phagocytosis.

Immune cells that kill virus-infected cells by inducing programmed cell death.

Soluble proteins that play multiple roles in the immune response, including recruiting immune cells to the site of infection, opsonizing bacteria to enhance phagocytosis, and forming membrane attack complexes to poke holes in bacterial membranes.

Localized immune response characterized by redness, heat, swelling, and pain, caused by the recruitment of immune cells to the site of infection.

Ability of the immune system to remember and mount a faster and stronger response upon re-exposure to a previously encountered pathogen.

Lymphocytes that play a crucial role in the adaptive immune response, including helper T-cells that activate macrophages and B cells, and killer T-cells that directly kill virus-infected cells.

Lymphocytes that differentiate into plasma cells, which secrete antibodies that can opsonize pathogens, activate complement, and neutralize toxins.

Specialized tissues, including lymph nodes, spleen, and tonsils, where immune cells are concentrated to facilitate immune responses.