Immune Response Cheat Sheet

The core ideas of Immune Response distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Innate Immunity

The body's first line of defense, present from birth, providing rapid but nonspecific protection. It includes physical barriers (skin, mucous membranes), chemical defenses (stomach acid, enzymes in tears), and cellular responses (phagocytes, natural killer cells, inflammation).

Adaptive Immunity

A highly specific immune response that develops after exposure to a pathogen. It involves lymphocytes (B cells and T cells) that recognize specific antigens and create immunological memory for faster, stronger responses to future encounters.

Antigens and Antibodies

Antigens are molecules (usually proteins) on the surface of pathogens that the immune system recognizes as foreign. Antibodies are Y-shaped proteins produced by B cells that bind specifically to antigens, marking pathogens for destruction or neutralizing them directly.

T Cells (Cell-Mediated Immunity)

Lymphocytes that mature in the thymus and coordinate the adaptive immune response. Helper T cells activate B cells and other immune cells by releasing cytokines. Cytotoxic (killer) T cells directly destroy infected host cells by recognizing antigens presented on cell surfaces.

Immunological Memory

After an infection is cleared, a subset of B and T cells become long-lived memory cells. Upon re-exposure to the same pathogen, these memory cells enable a secondary immune response that is faster, stronger, and longer-lasting than the primary response.

B Cells (Humoral Immunity)

Lymphocytes that mature in the bone marrow and are responsible for antibody-mediated (humoral) immunity. When activated by an antigen and helper T cells, B cells differentiate into plasma cells that secrete antibodies and memory B cells that provide long-term protection.

Phagocytes

White blood cells of the innate immune system that engulf and digest pathogens, dead cells, and debris through phagocytosis. The main types are neutrophils (fast-acting first responders) and macrophages (longer-lived cells that also present antigens to activate adaptive immunity).

Inflammation

A nonspecific innate immune response triggered by tissue damage or infection. Damaged cells release histamine and other chemical signals that dilate blood vessels and increase their permeability, producing the classic signs of redness, warmth, swelling, and pain while recruiting immune cells to the site.

Key Terms at a Glance

Innate Immunity:The nonspecific, immediate defense system present from birth, including physical barriers (skin, mucous membranes), chemical defenses (stomach acid, lysozyme), and cellular responses (phagocytes, inflammation, natural killer cells).

Adaptive Immunity:The specific, acquired defense system that develops after exposure to pathogens, involving B cells and T cells that target particular antigens and create immunological memory for future encounters.

Antigen:A molecule, typically a protein or polysaccharide on a pathogen's surface, that the immune system recognizes as foreign and that triggers an immune response.

Antibody:A Y-shaped protein (immunoglobulin) produced by plasma cells that binds specifically to an antigen, neutralizing the pathogen or marking it for destruction by other immune cells.

B Cell:A lymphocyte that matures in the bone marrow and is responsible for humoral (antibody-mediated) immunity. When activated, B cells differentiate into antibody-secreting plasma cells and long-lived memory B cells.

T Cell:A lymphocyte that matures in the thymus. Helper T cells (CD4+) coordinate immune responses via cytokines. Cytotoxic T cells (CD8+) directly kill infected host cells by recognizing antigens on MHC class I molecules.

Phagocyte:An immune cell that engulfs and digests pathogens through phagocytosis. Major types include neutrophils (rapid first responders) and macrophages (longer-lived cells that also present antigens).

Inflammation:A nonspecific innate response to tissue damage or infection, characterized by redness, warmth, swelling, and pain caused by histamine-mediated vasodilation and increased vascular permeability.

Immunological Memory:The ability of the adaptive immune system to remember previously encountered pathogens through long-lived memory B and T cells, enabling faster and stronger secondary responses.

Plasma Cell:A short-lived, terminally differentiated B cell that produces large quantities of antibodies (up to 2,000 per second) during an active immune response.

MHC (Major Histocompatibility Complex):Cell surface molecules that display protein fragments for immune surveillance. MHC class I (on all nucleated cells) presents intracellular antigens to cytotoxic T cells. MHC class II (on antigen-presenting cells) presents extracellular antigens to helper T cells.

Cytokine:A signaling protein released by immune cells (especially helper T cells) that regulates the immune response by activating, recruiting, or suppressing other immune cells.

Vaccination:The administration of harmless antigens (weakened, inactivated, or partial pathogens) to stimulate adaptive immunity and create memory cells without causing disease, providing protection against future infection.

Autoimmune Disease:A condition in which the immune system mistakenly attacks the body's own healthy cells and tissues, resulting from a failure of self-tolerance mechanisms. Examples include Type 1 diabetes, multiple sclerosis, and lupus.

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