Responding to Antigens

Vocabulary flashcards covering key terms from the lecture notes on the immune system and antigen response.

Innate immunity

The non-specific defence active from birth; immediate response; lacks immunological memory and forms part of the 2nd line of defence.

Adaptive immunity

The specific defence developing targeted responses with memory; involves T and B cells and antibodies (3rd line of defence).

1st line of defence

External barriers that prevent pathogen entry, including physical, chemical, and microbiological barriers in animals (and physical/chemical barriers in plants).

2nd line of defence

The innate immune system; non-specific responses including interferons, the complement system, fever, inflammatory cells, and phagocytosis.

3rd line of defence

The adaptive immune system; specific responses and memory, involving antibodies and lymphocytes.

Lysozyme

Antimicrobial enzyme in tears, saliva, and other secretions that helps break down bacterial cell walls.

Phytoalexin

Plant-produced antimicrobial toxins produced in response to infection.

PAMP

Pathogen-associated molecular pattern; conserved pathogen molecules recognized by pattern recognition receptors to trigger innate immunity.

DAMP

Damage-associated molecular pattern; host-derived molecules released by damaged cells that trigger innate responses.

APC (Antigen Presenting Cell)

Cells (e.g., dendritic cells, macrophages, B cells) that process and present antigen on MHC to T cells.

MHC I

Major histocompatibility complex class I; presents endogenous antigen to CD8+ cytotoxic T cells; expressed on nearly all nucleated cells.

MHC II

Major histocompatibility complex class II; presents exogenous antigen to CD4+ helper T cells; expressed on APCs.

Antigen

A molecule or fragment recognized by the immune system; can be self or non-self.

Antigen presentation

Display of antigen fragments on MHC molecules by APCs to T cells, initiating adaptive responses.

Self-antigen

Antigen derived from the host's own tissues; not targeted as foreign.

Non-self antigen

Antigen derived from pathogens or foreign sources that trigger an immune response.

PRR

Pattern Recognition Receptor; receptors on phagocytes that detect PAMPs or DAMPs to activate innate responses.

Phagocytosis

Engulfment and digestion of pathogens or debris by phagocytes (e.g., neutrophils, macrophages, dendritic cells).

Phagosome

Vesicle formed around ingested material inside a phagocyte.

Phagolysosome

Fusion of a phagosome with a lysosome where digestion occurs.

Inflammation

Protective response to infection or damage involving vascular, cellular, and resolution stages with redness, heat, swelling, pain, and sometimes pus.

Vascular stage

Early inflammation with vasodilation and increased blood flow, mediated by signals like histamine.

Cellular stage

Recruitment and activation of leukocytes at the site of infection or damage.

Resolution stage

Termination of inflammation and healing; anti-inflammatory mediators promote repair.

Interferons

Cytokines produced by host cells in response to viral infection; inhibit viral replication and alert neighboring cells.

Complement system

Cascade of plasma proteases that enhances antibodies and phagocytes; promotes opsonisation, chemotaxis, and lysis via MAC.

Opsonisation

Coating of a pathogen with opsonins (antibodies or C3b) to enhance phagocytosis.

Chemotaxis

Movement of leukocytes toward the site of infection guided by chemical signals.

MAC (Membrane Attack Complex)

Complex of complement proteins that forms pores in bacterial membranes causing lysis.

Fever

Systemic rise in body temperature during infection that enhances immune defence and inhibits pathogen growth.

Neutrophil

A short-lived phagocytic white blood cell that rapidly responds to infection.

Macrophage

Phagocytic cell that engulfs pathogens and presents antigens via MHC II; tissue resident.

Dendritic cell

Potent APC that processes and presents antigen to T cells, bridging innate and adaptive immunity.

NK cell

Natural killer cell; innate cytotoxic lymphocyte that destroys virally infected or cancerous cells via degranulation.

Mast cell

Innate cell that releases histamine and other mediators during degranulation to promote inflammation.

Eosinophil

Granulocyte that targets parasites and participates in allergic responses; degranulates releasing toxic substances.

Basophil

Blood cell that releases histamine and cytokines during degranulation; involved in allergic inflammation.

Degranulation

Release of granule contents (histamine, cytokines, prostaglandins, etc.) from innate immune cells.

Histamine

Mediator released by mast cells and basophils causing vasodilation and increased vascular permeability.

Cytokines

Small signaling proteins coordinating immune responses (includes interferons and interleukins).

Interleukins

Cytokines produced by leukocytes that regulate communication between immune cells.

Prostaglandins

Inflammatory mediators (eicosanoids) contributing to pain, fever, and vascular changes.

Diapedesis

Movement of leukocytes through the endothelium from blood into tissues.

B cell

Lymphocyte producing antibodies; can present antigen via MHC II and participate in humoral immunity.

Lymph node

Secondary lymphoid organ where APCs present antigens to T and B cells to activate adaptive immunity.