UNIT 4 AOS 1 RESPONDING TO ANTIGENS

LYMPHOID TISSUE

a specialized connective tissue that forms the structural basis of the immune system. Primarily composed of lymphocytes (white blood cells) and reticular fibers, it traps pathogens, produces antibodies, and filters body fluids.

LYMPH VESSELS

a branching network of thin-walled, valve-equipped tubes that collect excess interstitial fluid (lymph) from your tissues and return it to your bloodstream.

SPLEEN

a small, fist-sized organ located in the upper left part of your abdomen, under the rib cage and behind the stomach. It is a crucial part of the immune system and works to filter blood, fight infections, and store blood cells.

THYMUS

a small, specialized organ of the immune and lymphatic systems located in the upper chest behind the breastbone. Its primary function is to mature white blood cells called T-lymphocytes (T-cells), which are essential for fighting infections, viruses, and cancer.

BONE MARROW

a soft, spongy tissue found inside the hollow centers of bones. It serves as the body's primary blood cell factory, producing billions of red blood cells, white blood cells, and platelets daily to carry oxygen, fight infection, and control bleeding.

INNATE IMMUNITY

a response to a pathogen that is not specific to the antigen, only that it has been identified as being non-self; the response does not generate antibodies or memory lymphocytes.

ADAPTIVE IMMUNITY

an immune response directed against a specific antigen; it retains memory of that antigen so that, on subsequent exposure to the same antigen, it responds with a secondary response.

NON-SPECIFIC

a response that is the same regardless of the type of antigen.

PHYSICAL BARRIERS

are the first line of defence in the innate immune system. They prevent pathogens from entering the body or trap them so they can be easily expelled or destroyed. Examples include intact skin, cilia, mucous membranes.

CHEMICAL BARRIERS

are part of the innate first line of defence. They use specialised fluids, acids, and enzymes to create hostile environments or directly destroy pathogens' cell walls. This includes stomach acid, lysozymes, sweat etc.

MICROBIOTA BARRIERS

a first-line defence in animals where non-pathogenic, beneficial bacteria (normal flora) prevent harmful pathogens from colonising the body. Examples include the digestive tract gut bacteria, skin bacteria etc.

PHAGOCYTES

a cell that is capable of phagocytosis; includes macrophages, dendritic cells and neutrophils.

NK (NATURAL KILLER) CELLS

a type of white blood cell (lymphocyte) that circulates in the blood and patrols the body to identify and destroy compromised cells, such as virally infected cells and cancerous tumor cells. Apart of the innate immune system.

COMPLEMENT

a number of small proteins found in the blood that, when activated, promote chemotaxis, cell lysis and phagocytosis.

INTERFERON

a type of cytokine produced by the cells of the immune system in response to challenges by foreign agents such as viruses, bacteria, parasites and tumour cells.

CYTOKINE

a signalling molecule that coordinates inflammation and immune responses and that leukocytes use to communicate with one another; includes interleukins and interferons.

INFLAMMATION

an innate response to infection or damage that causes pain, swelling, heat and redness.

LEUKOCYTES

the general term for a white blood cell

NEUTROPHILS

a phagocytic leukocyte found in the blood and tissues

MACROPHAGES

a large white blood cell that phagocytoses pathogens; originates as monocytes in circulation

MONOCYTES

Monocytes are the largest type of white blood cell. As a key component of the innate immune system (second line of defense), they circulate in the blood. When an infection occurs, they migrate into tissues and differentiate into specialised cells like macrophages and dendritic cells.

EOSINOPHILS

a leukocyte that secretes powerful enzymes capable of rupturing multicellular organisms

CHEMOKINES

a type of cytokine that induces chemotaxis

PHAGOSOMES

a membrane-bound vesicle formed around a particle during phagocytosis

PHAGOLYSOSOME

a membrane-bound vesicle formed from the fusion of a phagosome and lysosome.

PERFORIN

a pore-forming protein released by cytotoxic T cells and Natural Killer (NK) cells. It punches holes in the plasma membranes of infected or cancerous cells, allowing granzymes to enter the cell and trigger programmed cell death (apoptosis).

ANTIGEN

a large molecule, usually a protein or polysaccharide, that generates an immune response

CYTOTOXIC IMMUNE CELLS

are part of the adaptive immune response. Their main role is to target and destroy abnormal or infected cells (intracellular threats) by inducing apoptosis.

MHC I & II

are essential cell-surface proteins that VCE Biology uses to distinguish "self" from "non-self". They act as structural platforms that present antigens to the adaptive immune system.

MHC I is found on all nucleated cells. They act as "self" identification tags and constantly display bits of protein from inside the cell. If a cell is healthy, it presents "self" antigens. If a cell is infected or cancerous, it presents "non-self" (foreign) antigens, triggering Cytotoxic T cells to destroy it

MHC II molecules are protein markers found exclusively on professional Antigen-Presenting Cells (APCs). Their main job is to engulf extracellular pathogens, digest them, and display the foreign antigen fragments on the cell surface so they can be recognised by Helper T cells.

DEGRANULATION

a cellular process in which the granules of neutrophils, mast cells, basophils or eosinophils are emptied into extracellular surroundings.

COMPLEMENT CASCADE

an innate immune mechanism comprising circulating blood proteins that activate one another in a domino-like sequence. It targets pathogens by aiding in opsonisation (tagging for phagocytosis), inflammation (attracting white blood cells), and cytolysis (punching holes in bacterial cell membranes via the Membrane Attack Complex).

OPSONISATION

the immune process where pathogens are coated with molecules called opsonins (like antibodies or complement proteins), acting as "tags". This allows macrophages and neutrophils to easily recognise, bind to, and engulf the pathogen via phagocytosis.

MEMBRANE ATTACK COMPLEX

a structure formed by blood-borne complement proteins. As a key part of the innate immune system, these proteins assemble on the surface of invading pathogens, punching pores in their cell membranes to cause lysis (bursting) and cell death.

ACUTE

an "acute" immune response refers to the fast-acting, short-term innate response to tissue damage or pathogens; such as the inflammatory response.

HISTAMINE

a chemical released by mast cells and basophils that increases blood flow and the permeability of capillaries.

MAST CELL

a cell that is located in the tissues and releases granules containing histamines when activated.

PLATELETS

a cell fragment found in the blood involved in blood clotting.

ANGIOGENESIS

Angiogenesis is the process by which new blood vessels form from pre-existing ones.

SPECIFICITY

adaptive (third) line of defense’s ability to target highly specific antigens (foreign markers). Each lymphocyte (B cell or T cell) has unique receptors designed to match and respond to only one specific antigenic shape, like a lock fitting a single key.

LYMPHOCYTES

Lymphocytes are the white blood cells responsible for your body's specific (adaptive) immune response. Found in the bloodstream and lymphatic system, they recognise specific foreign antigens.

B CELLS

are white blood cells of the adaptive immune system responsible for humoral immunity. They mature in the bone marrow, patrol the body's fluids, and produce highly specific antibodies to neutralise pathogens like bacteria, viruses, and toxins

APC (ANTIGEN PRESENTING CELL)

is an immune cell that engulfs a pathogen, digests it, and displays the foreign antigen on its surface using MHC Class II markers. This presentation activates the adaptive immune system. These include dendritic cells, macrophages, and B cells.

DENDRITIC CELL

a phagocyte with membranous extensions that engulf pathogens, process them and present them to other cells of the immune system.

IgE

is an antibody primarily responsible for allergic reactions. It triggers the immune system to overreact to harmless substances (allergens).

ALLERGY

is a hypersensitive, overreactive immune response to a typically harmless substance (an allergen).

ANAPHALAXIS

It occurs when a pre-sensitised immune system overreacts to a normally harmless substance (allergen). This triggers a massive, systemic release of inflammatory chemicals, causing rapid constriction of the airways and a dangerous drop in blood pressure.

PLASMA CELLS

specialised, terminally differentiated B lymphocytes. Their sole, powerful function in the immune system is to act as "factories" that mass-produce and secrete millions of complementary antibodies to neutralise specific pathogens during the humoral adaptive immune response.

ANTIBODIES

specialized, Y-shaped proteins produced by B lymphocytes (plasma cells) in the humoral immune response. They bind to specific non-self antigens, forming an antigen-antibody complex to deactivate pathogens and mark them for destruction by phagocytes.

GRANZYME

enzymes released by cytotoxic T cells and Natural Killer (NK) cells. Once inside a target cell, they trigger apoptosis (programmed cell death) to eliminate virus-infected or cancerous cells.

PERFORIN

is a pore-forming protein released by cytotoxic T cells (CD8+) and Natural Killer (NK) cells to destroy infected or cancerous body cells.

AUTOIMMUNE RESPONSE

An autoimmune disease occurs when the immune system fails to recognize the body's own markers (self-antigens) and mistakenly attacks healthy cells, tissues, or organs.

CHEMOKINE

a type of cytokine that induces chemotaxis.