MLS Immunology Chapter 1: Elements of the Immune System and Their Roles in Defense

Vocabulary flashcards covering core concepts, cell types, physical barriers, innate vs. adaptive immunity, phagocytosis, antibodies, MHC molecules, and lymphoid organs from the MLS Immunology lecture.

Immunology

The study of physiological mechanisms used to defend the body from invasion by foreign or infectious agents.

Vaccination

The procedure that exposes healthy individuals to a harmless or attenuated form of a microorganism to induce protective immunity without causing disease.

Edward Jenner

The physician who discovered in 1796 that inoculation with cowpox (vaccinia virus) protected against human smallpox (Variola virus).

Opportunistic pathogens

Microorganisms that typically cause no harm but produce disease if the host's body defenses are weakened or if they enter an atypical body site.

Commensal species

Microorganisms, such as normal gut flora, that inhabit host tissues and consume nutrients without causing harm to the host.

Epithelium

Layers of specialized cells lining the outer surface and inner cavities of the body, serving as a primary physical barrier to infection.

Mucus

A thick protective fluid containing glycoproteins, proteoglycans, and enzymes that coats mucosal surfaces.

Defensins

Antimicrobial peptides produced by epithelia that kill bacteria, fungi, and enveloped viruses by disrupting their membranes.

Lysozyme

An antibacterial enzyme present in tears and saliva that constitutes approximately $40\%$ of total tear protein.

Innate immune response

The rapid, immediate, and genetically programmed defense mechanism consisting of pathogen recognition and effector cell recruitment.

Cytokines

Small messenger proteins secreted by infected or damaged cells that signal and activate effector immune cells.

Inflammation

A localized immune response characterized by heat, redness, swelling, and pain caused by increased blood vessel permeability and cell recruitment.

Edema

Tissue swelling resulting from the leakage of blood plasma through permeable vascular walls into tissue during inflammation.

Complement

A system of plasma proteins that tags pathogens for phagocytosis or directly destroys them by forming membrane pores.

Primary immune response

The adaptive immune response elicited when the body encounters a specific pathogen for the first time, involving a lag phase of approximately $7\text{ days}$.

Secondary immune response

The rapid and augmented adaptive immune response triggered upon re-exposure to a pathogen previously encountered.

Clonal selection

The process by which a specific antigen binds to and activates only the individual lymphocyte expressing a complementary receptor.

Clonal expansion

The rapid proliferation and differentiation of an antigen-selected lymphocyte into a large clone of specific effector cells.

Hematopoiesis

The continuous generation of blood cells from pluripotent hematopoietic stem cells in the body.

Yolk sac

The initial anatomical site of hematopoiesis in the early human embryo.

Fetal liver and spleen

The primary anatomical sites of hematopoiesis in the human fetus between months $3$ and $7$ of gestation.

Leukocytes

A general term for all white blood cells, including granulocytes, monocytes, and lymphocytes.

Neutrophils

The most abundant leukocytes ($40\%$–$75\%$ of white blood cells), specialized as short-lived phagocytes that function in anaerobic conditions and form pus upon death.

Monocytes

Circulating leukocyte precursors ($2\%$–$10\%$ of white blood cells) that migrate into tissues to differentiate into macrophages.

Macrophages

Large tissue-resident phagocytic cells responsible for engulfing microorganisms, secreting inflammatory cytokines, and activating T cells.

Dendritic cells

Star-shaped antigen-presenting cells that carry ingested pathogens from tissues to draining lymph nodes to activate T cells.

Mast cells

Tissue-resident cells containing histamine-filled granules that mediate vasodilation, vascular permeability, and expulsion of parasites.

Eosinophils

Granulocytes ($1\%$–$6\%$ of white blood cells) with red-staining granules specialized in extracellular killing of antibody-coated parasites.

Basophils

Rare circulating granulocytes ($<1\%$ of white blood cells) containing basic blue-staining granules that control immune responses to parasites.

Natural killer (NK) cells

Large granular lymphocytes of innate immunity ($5\%$–$10\%$ of circulating lymphocytes) that kill virus-infected cells and secrete cytokines.

Small lymphocytes

Resting, naïve adaptive immune cells ($20\%$–$50\%$ of white blood cells) comprising B cells and T cells.

Plasma cell

A terminally differentiated form of B cell dedicated to synthesizing and secreting large quantities of antibodies.

Megakaryocytes

Large lobulated bone marrow cells whose cytoplasm fragments to form blood platelets under regulation by thrombopoietin.

Erythrocytes

Red blood cells responsible for oxygen transport and binding immune complexes for clearance by Kupffer cells in the liver.

Kupffer cells

Specialized phagocytic macrophages residing in the liver that line hepatic sinusoids to clear immune complexes.

Microglia

Specialized macrophage-like phagocytic cells located within the central nervous system.

Pseudopodia

Membrane evaginations extended by phagocytes to bind and ingest bacterial targets.

Phagosome

An intracellular endocytic membrane-bound vesicle formed around an ingested microorganism during phagocytosis.

Phagolysosome

An acidic digestive organelle formed by the fusion of a phagosome with a lysosome, containing toxic molecules and hydrolytic enzymes.

Opsonization

The coating of pathogen surfaces by antibodies or complement fragments to enhance recognition and ingestion by phagocytes.

Antigen

Any molecule or molecular fragment capable of being specifically bound by an antibody or T-cell receptor.

Epitope

The specific structural portion or determinant of an antigen recognized and bound by an antigen receptor.

Neutralization

The antibody mechanism of binding directly to a pathogen or toxin to prevent interaction with host cell receptors.

MHC class I

Cell surface proteins expressed on all nucleated cells that present intracellular peptides to CD8 cytotoxic T cells.

MHC class II

Cell surface proteins expressed on professional antigen-presenting cells that present extracellular peptides to CD4 helper T cells.

Primary lymphoid tissues

Anatomical sites where lymphocytes undergo maturation, consisting of the bone marrow (for B cells) and the thymus (for T cells).

Secondary lymphoid tissues

Anatomical sites, such as lymph nodes, spleen, and MALT, where mature lymphocytes encounter antigens and initiate immune responses.

White pulp

The secondary lymphoid region of the spleen surrounding central arterioles, composed of PALS and B-cell coronas, where blood-borne pathogens encounter lymphocytes.

Red pulp

The non-lymphoid splenic tissue responsible for filtering and removing aged or damaged red blood cells from circulation.

M cells

Specialized microfold cells in gut-associated lymphoid tissue (GALT) that deliver intact luminal pathogens across the epithelial layer to underlying immune cells.