A clean, simplified medical study infographic titled "Human Antibodies - Quick Reference" with a white background, organized into 4 sections: SECTION 1 - "Immunoglobulin Structure" (top left, light blue background): A simple Y-shaped antibody diagram showing: - Heavy chains (γ, α, μ, δ, ε) on the sides - Light chains (Kappa κ, Lambda λ) in the middle - Variable region (antigen binding) at tips - Constant region at base - Labels: Fc region (bottom), Fab region (top arms) SECTION 2 - "5 Immunoglobulin Classes" (top right, light pink background): A clean table with 5 rows: IgG | Most abundant | Crosses placenta | Half-life 23 days IgA | Found in secretions/milk | J chain | Half-life 5-7 days IgM | First in infection | Pentamer | Highest concentration in blood IgD | On lymphocyte surface | First antibody secreted IgE | Allergic reactions | Lowest concentration (0.00002 mg/mL) SECTION 3 - "Cell-Mediated vs Humoral Immunity" (bottom left, light green background): Two columns: LEFT: Cell-Mediated (T-cells) - thymus-derived, initiate immune responses, T:B ratio = 3:1 RIGHT: Humoral (B-cells) - bursa-equivalent, antibody molecules, immunoglobulins SECTION 4 - "MHC Classes" (bottom right, light yellow background): Class I: HLA-A, B, C | on all nucleated cells | TCR recognition Class II: HLA-DP, DQ, DR | on antigen presenting cells | T-cell activation Note: Highly polymorphic, chromosome 6, co-dominant Clean sans-serif fonts, color-coded boxes, simple icons, medical textbook style, no clutter