Immunology — Clear Glass Compendium

Immunology

The immune system is an intricate network of barriers, cells, organs, and soluble mediators that distinguishes self from non-self, destroys threats, and restores homeostasis. When regulation fails, the same machinery drives allergy, autoimmunity, or immunodeficiency.

Anatomical Organization

Category	Components	Principal Functions
Primary (central) lymphoid organs	Bone marrow, thymus	Hematopoiesis; B-cell maturation; T-cell selection (positive/negative)
Secondary (peripheral) lymphoid organs	Lymph nodes, spleen, MALT (Peyer’s patches), tonsils, adenoids	Antigen presentation; clonal expansion; germinal-center reactions (class-switch, affinity maturation)
Tertiary (inducible) lymphoid structures	Ectopic follicles during chronic infection/autoimmunity	Localized adaptive responses; antibody diversification in diseased tissues

Barrier tissues—skin and mucosa of the respiratory, GI, and GU tracts—combine tight junctions with antimicrobial peptides, lysozyme, mucus, cilia, and commensal microbiota to repel invaders.

Immune Anatomy — Overview

Innate Immune Cells (germline-encoded recognition)

Cell	Key Receptors	Effector Functions
Neutrophils	PRRs (e.g., TLRs), FcγR	Phagocytosis; ROS; neutrophil extracellular traps (NETs)
Monocytes / Macrophages	PRRs, complement receptors	Phagocytosis; cytokine secretion; antigen presentation; tissue repair (M2)
Dendritic cells (DCs)	High-density PRRs	Professional APCs; migrate to nodes; prime naive T cells
Natural killer (NK) cells	Activating & inhibitory NKRs; CD16 (FcγRIII)	Perforin/granzyme cytotoxicity; ADCC via CD16; cytokine production (IFN-γ)
Innate lymphoid cells (ILC1-3)	Cytokine receptors	Rapid cytokine release mirroring Th1/Th2/Th17 programs; barrier defense and repair

NK cells exemplify innate cytotoxic effectors—killing virally infected or transformed cells and mediating antibody-dependent cellular cytotoxicity via CD16.

Adaptive Immune Cells (somatically diversified)

Cell	Key Features	Primary Roles
B lymphocytes	BCR; class-switch recombination; somatic hypermutation	Secrete antigen-specific antibodies; memory B cells; plasma cells
CD4⁺ T cells	TCR + MHC II; subsets Th1/Th2/Th17/Tfh/Treg	Cytokine “orchestration,” help for B cells, macrophage activation, tolerance
CD8⁺ cytotoxic T cells	TCR + MHC I	Perforin/granzyme-mediated killing of infected or malignant cells

V(D)J recombination builds a vast receptor repertoire; germinal centers refine specificity via somatic hypermutation and affinity selection.

Humoral & Cellular Effector Arms

Arm	Components	Key Notes
Humoral	Antibodies (IgM→IgG/IgA/IgE), complement (classical/lectin/alternative)	Neutralization, opsonization, complement-mediated lysis; mucosal IgA; IgE–mast cell axis in allergy/helminths
Cellular	CD8⁺ CTLs, Th1-activated macrophages, NK cells	Intracellular pathogen control; tumor surveillance; granuloma formation in persistent infections

Immunopathology

Category	Representative Conditions	Mechanism
Hypersensitivity	Type I (anaphylaxis), II (autoimmune hemolytic anemia), III (serum sickness), IV (contact dermatitis)	IgE-mediated mast-cell degranulation; antibody/complement cytotoxicity; immune-complex deposition; T-cell–mediated inflammation
Autoimmune disease	SLE, rheumatoid arthritis, type 1 diabetes	Loss of self-tolerance; genetic (HLA, CTLA-4), hormonal, and environmental triggers
Immunodeficiency	Primary (SCID, CVID), Secondary (HIV, chemotherapy)	Defects in lymphocyte development/function or iatrogenic depletion

Homeostasis & Regulation

Mechanism	How It Maintains Balance
Central & peripheral tolerance	Negative selection in thymus/BM; Tregs and anergy prevent autoreactivity
Checkpoint molecules	CTLA-4/PD-1 dampen T-cell activation; therapeutic blockade boosts antitumor immunity but risks autoimmunity
Resolution programs	IL-10, TGF-β, specialized pro-resolving mediators (SPMs) restore tissue equilibrium after pathogen clearance

At a Glance — Key Takeaways

Innate immunity provides rapid pattern-based defense; adaptive immunity yields precision and memory.
Germinal centers are engines of antibody affinity and class specialization.
Misregulated immunity underlies allergy, autoimmunity, cancer immunity, and infection susceptibility.
Barrier integrity and the microbiome are frontline determinants of immune tone.

Educational overview; not a substitute for medical care.