Module 1: Immunity & Immune System

Immunology

The study of the immune system and the body's mechanisms to resist infection and react to foreign substances.

Immunity

The ability of the body to resist infection through normally present nonspecific functions or acquired specific responses.

Antigen

A foreign substance that can induce a host immune response or bind specifically with antibodies and immune receptors.

Attenuation

The process of weakening pathogens to produce vaccines, developed by Dr. Louis Pasteur.

15th Century Smallpox Inhalation

Early attempt in China and Turkey where individuals inhaled powder from smallpox scabs to induce immunity.

Dr. Edward Jenner

Scientist in the 1700s who developed the smallpox vaccine using cowpox material.

Dr. Louis Pasteur

Known as the "Father of Immunology" for developing multiple vaccines through attenuation in the 1800s.

Elie Metchnikoff

Pioneer who discovered cell-based immunity and phagocytosis.

Emil von Behring

Pioneer who discovered humoral-based immunity.

Almroth Wright

Scientist who linked cell-based and humoral-based immunity theories together.

Innate Immunity (Natural Immunity)

Nonspecific protection present at birth that acts immediately without prior antigen exposure or memory generation.

Adaptive Immunity (Acquired Immunity)

Antigen-specific protection mediated by lymphocytes that requires exposure and generates immunological memory.

Hematopoiesis

The formation of blood cells in bone marrow where hematopoietic stem cells (HSCs) differentiate into myeloid (CMP) and lymphoid (CLP) precursors.

Common Myeloid Precursors (CMP)

Precursors in bone marrow that give rise to granulocytes, monocytes, macrophages, and most dendritic cells.

Common Lymphoid Precursors (CLP)

Precursors in bone marrow that give rise to B cells, T cells, and Natural Killer (NK) cells.

Erythropoietin

Cytokine/growth factor that stimulates red blood cell (RBC) production during hematopoiesis.

Neutrophils (PMNs)

Most abundant WBCs (50%–70%) containing multi-lobed nuclei and neutral granules; primary function is phagocytosis.

Eosinophils

WBCs (1%–4%) with bi-lobed nuclei and red-orange granules; function in phagocytosis, neutralizing allergic products, killing parasites, and releasing cytokines.

Basophils

Rare WBCs (<1%) with bi-lobed nuclei and deep blue-purple granules; release histamine to induce and maintain allergic reactions.

Mast Cells

Tissue-resident cells in skin and connective tissue derived from a separate lineage than basophils; induce and maintain allergic responses.

Monocytes

Peripheral blood WBCs (2%–10%) with horseshoe-shaped nuclei that migrate into tissues to become macrophages.

Macrophages

Tissue-resident cells derived from monocytes; perform innate phagocytosis, microbial killing, tumor eradication, and present antigens to T cells.

Dendritic Cells

Leukocytes with long membranous extensions; recognized as the most potent phagocytic cells and most effective antigen-presenting cells (APCs).

Phagocytic Leukocytes

White blood cells capable of phagocytosis: neutrophils, monocytes, macrophages, and dendritic cells.

Lymphocytes

Peripheral WBCs (20%–40%) with large round nuclei and sparse cytoplasm; include B cells, T cells, and NK cells.

B Cells

Lymphocytes that mature in bone marrow, express surface Ig, CD19, CD20, and CD21, and differentiate into antibody-secreting plasma cells.

Plasma Cells

Fully differentiated B cells with eccentric oval nuclei that actively secrete antibodies.

T Cells

Lymphocytes that mature in the thymus and express the CD3 surface marker.

Helper T Cells (TH)

CD4+ T cells that secrete cytokines to stimulate B cell antibody production and assist in cell-mediated immunity.

Regulatory T Cells (Treg)

CD4+ T cells responsible for inhibiting immune responses.

Cytotoxic T Cells (TC)

CD8+ T cells that directly destroy tumor cells and virus-infected cells.

Natural Killer (NK) Cells

Innate granular lymphocytes (CD16+, CD56+) that kill virus-infected and tumor cells without prior antigen exposure.

Primary Lymphoid Organs

Bone marrow and thymus; structural locations where lymphocyte maturation occurs.

Secondary Lymphoid Organs

Lymph nodes, spleen, MALT, and SALT; sites where mature lymphocytes contact foreign antigens and become activated.

Lymph Node Architecture

Organized into cortex (B cells in primary/secondary follicles), paracortex (T cells), and medulla.

Spleen Anatomy

Consists of Red Pulp (rich in macrophages to destroy old RBCs) and White Pulp (PALS containing T cells with attached B cell follicles).

MALT & SALT

Mucosal-Associated Lymphoid Tissue (tonsils, appendix, Peyer's patches) and Skin-Associated Lymphoid Tissue serving as major antigen entry barriers.