Body Defenses and Immunity

Flashcards covering the vocabulary and key concepts of the human immune system, including nonspecific and specific defenses, cell types, and immune responses.

Nonspecific (innate) defense system

A system that responds immediately to protect the body from foreign substances; includes external membranes like skin and mucosa, as well as inflammation, phagocytes, and antimicrobial proteins.

Specific (adaptive) defense system

Also known as the Immune System, it mounts attacks against foreign substances using macrophages and lymphocytes; it is characterized by antigen-specificity, systemic action, and memory.

Keratin

A protein found in the epidermis that acts as a physical barrier resistant to weak acids, bases, bacterial enzymes, and toxins.

Lysozyme

An antibacterial enzyme found in saliva and lacrimal fluid (tears).

Phagocytes

Cells, mainly macrophages arising from monocytes, that function by engulfing foreign bodies (phagocytosis) and sometimes engaging in a respiratory burst.

Opsonization

The process of coating a foreign substance with proteins (usually complement proteins) to provide a place for attachment, making phagocyte adhesion possible.

Natural Killer (NK) cells

Non-phagocytic cells located in blood and lymph that lyse and kill cancer or virus-infected cells by attacking the cell membrane and releasing cytolytic enzymes called perforins.

Vasodilation

The widening of arterioles in a damaged area during inflammation, which increases blood flow and leads to redness and heat (warmth).

Edema

Local swelling resulting from increased permeability of local capillaries, which allows fluid to enter interstitial spaces.

Margination

The process where neutrophils stick to the endothelial wall of capillaries by attaching to cell adhesion molecules (CAMs) called selectins.

Diapedesis

The process by which neutrophils squeeze through capillary walls to reach damaged tissue.

Positive chemotaxis

The movement of neutrophils or other WBCs toward a damaged area by following a chemical trail left by injured cells.

Complement proteins

A group of at least $20$ plasma proteins that circulate in an inactive state; when activated, they amplify inflammation, cause cell lysis, and enhance phagocytosis through opsonization.

Interferons

Proteins released by virus-infected cells that stimulate uninfected cells to produce PKR, a protein that inhibits viral replication.

Pyrogen

A chemical released by leukocytes and macrophages in response to microorganisms that resets the body's thermostat to a higher temperature, causing fever.

Haptens

Also called incomplete antigens; small molecules that are not immunogenic on their own but can trigger an immune response when combined with body proteins.

Antigenic determinants

Specific parts of an antigen that are immunogenic and serve as the binding sites for free antibodies or lymphocytes.

MHC (major histocompatibility complex) proteins

Cell surface glycoproteins that mark a cell as self; Class 1 are found on all body cells, while Class 2 are only on certain cells like Antigen-Presenting Cells (APCs).

Immunocompetent

The ability of a lymphocyte to recognize a specific antigen by binding to it.

Antigen-Presenting cells (APC'S)

Cells including macrophages, dendritic cells, and B-cells that engulf and digest antigens, then display antigenic determinants on their surface near MHC proteins.

Clonal selection

The process triggered by a B cell combining with an antigen, causing the B cell to grow and multiply into a family of identical cells called a clone.

Plasma cells

Cells derived from B cell clones that produce antibodies and typically last for $4-5$ days.

Secondary immune response

The immune response to re-exposure to a previously encountered antigen; it is faster ($2-3$ day peak), more prolonged, and more effective than the primary response.

Artificially acquired active immunity

Immunity produced by a vaccine (dead or weakened strain) which activates the immune system and creates memory cells without making the person ill.

Ig G

The most abundant and diverse antibody class (75-85 \text{%}), which crosses the placenta and is the main antibody of the secondary and late primary immune responses.

PLAN

An acronym for antibody targets and functions: Precipitation, Lysis (via complement fixation), Agglutination, and Neutralization.

Cytokines

Proteins such as interleukins that influence cell development and differentiation in the immune system; includes lymphokines (from lymphocytes) and monokines (from macrophages).

Helper T (TH) cells

CD4 cells that act as managers of the immune response, activating macrophages, helping activate B and T cells, and inducing cell proliferation.

Cytotoxic T (Tc) cells

CD8 cells that directly attack and kill other cells using perforins, granzymes, and lymphokines.

Regulatory T (TReg) Cells

Formerly known as suppressor T cells, they slow or stop the activity of B cells and T cells once an infection is conquered.