Thymic Progenitor / Educating
Naive CD4+ Helper
Naive CD8+ Cytotoxic
Blood Pathogen
Neutralized Complex
Click canvas to inject localized antigen
Circulating Mature T-Cells 120 Emitted by Thymus
Blood Pathogen Load 0 CFU / mL equivalent
Splenic White Pulp Cleared 0 Phagocytosed & Neutralized
Systemic Immune Efficacy 99.4% Combined Clearance Rate
Thymus (Primary Lymphoid)
Central Tolerance

Site of T-cell receptor (TCR) somatic gene rearrangement and rigorous dual-stage tolerance education before systemic vascular release.

Thymic Cortex
Positive Selection: cTECs test TCR binding to self-MHC. Failures undergo apoptosis by neglect (90%+ eliminated).
94% Scrapped
Thymic Medulla
Negative Selection: mTECs express peripheral antigens via AIRE. Highly autoreactive thymocytes eliminated.
5% Auto-Purged
Corticomedullary Venules
Surviving immunocompetent, self-tolerant naive CD4+ & CD8+ T cells enter systemic circulation.
1-2% Qualified
Spleen (Secondary Lymphoid)
Blood Filter & Hub

The primary systemic immunological filter. Directly receives 5% of cardiac output, screening erythrocytes and entrapping blood antigens.

White Pulp (PALS & Follicles)
Periarteriolar lymphoid sheath concentrates thymic-derived naive T cells to scan dendritic-presented blood antigens.
Active Surveillance
Marginal Zone
Specialized macrophages and non-circulating B cells capture encapsulated bacteria (Streptococcus, Neisseria).
Opsonic Ready
Red Pulp (Splenic Cords)
Macrophage meshwork inspects RBC deformability, clears senescent cells, and recycles iron from hemoglobin.
Hemofiltration ON

The Essential Thymus-Spleen Axis

The immune system divides its architecture into Primary Lymphoid Organs (where lymphocytes are born and educated) and Secondary Lymphoid Organs (where educated lymphocytes encounter real-world pathogens).

The Thymus does not fight infections directly; instead, it serves as the master academy. Lymphoid progenitors travel from bone marrow into the thymic cortex. Through stochastic V(D)J recombination, every thymocyte crafts a unique T-cell receptor (TCR). The thymus subjects them to positive selection (confirming they can recognize host MHC molecules) and negative selection (eliminating thymocytes that attack healthy body proteins).

Once licensed, naive T cells migrate via the bloodstream directly to the Spleen. Unlike lymph nodes (which screen tissue fluid / lymph), the spleen is inserted directly into the vascular highway. Within the splenic white pulp, thymic T cells take up station along the periarteriolar lymphoid sheath (PALS), ready to detect circulating bacteremia or viremia within minutes of systemic entry.

Clinical Manifestations & Counterfactuals

Condition Organ Defect Systemic Consequence
DiGeorge Syndrome (22q11.2) Agenesis / hypoplasia of Thymus Profound deficiency of mature T cells; inability to mount cell-mediated immunity despite intact splenic architecture.
Post-Splenectomy Sepsis (OPSI) Surgical removal / infarction of Spleen Lifelong vulnerability to encapsulated pathogens (e.g. Streptococcus pneumoniae) due to loss of splenic marginal zone filtration.
Thymic Involution Age-associated fatty replacement Progressive decline in naive T-cell output; immune repertoire shifts to oligoclonal memory cells, impairing novel viral defense.
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