Comprehensive Immunology: Lymphatic System, Innate & Adaptive Immunity

Movement of lymph

Lymph flows from vessels → trunks → ducts → subclavian veins; returns fluid to blood

Importance of lymph return

Prevents edema, maintains blood volume, allows immune cell transport

Primary lymphoid organs

Red bone marrow (B cell maturation), thymus (T cell maturation)

Secondary lymphoid organs

Lymph nodes, spleen, MALT (tonsils, Peyer's patches)

Function of lymph nodes

Filter lymph, activate lymphocytes, trap pathogens

Function of spleen

Filters blood, removes old RBCs, immune response to blood antigens

Innate immunity definition

Immediate, nonspecific defense with no memory (barriers, phagocytes, NK cells, complement)

Adaptive immunity definition

Specific, slower first response, strong memory (B and T cells)

Three lines of defense

Barriers → innate internal defenses → adaptive immunity

Surface barrier function

Skin and mucous membranes block entry via keratin, mucus, lysozyme, acidity, defensins

Four cardinal signs of inflammation

Redness, heat, swelling, pain (due to vasodilation & increased permeability)

Helper T cell function (CD4)

Activate B cells, cytotoxic T cells, macrophages; coordinate immune response

Cytotoxic T cell function (CD8)

Kill infected or cancer cells using perforin and granzymes

Steps of T cell activation

APC presents antigen with MHC → costimulation → clonal expansion → effector + memory T cells

Role of MHC I

Present endogenous antigens to CD8 T cells

Role of MHC II

Present exogenous antigens to CD4 T cells

APCs examples

Dendritic cells, macrophages, B cells

B cell activation

Antigen binds BCR + helper T cell cytokines → plasma cells & memory cells

Plasma cell function

Secrete antibodies specific to antigen

IgM function

First antibody produced, strong agglutinator

IgA function

Mucosal immunity (saliva, tears, breast milk)

IgD function

B cell receptor

IgG function

Most abundant antibody; crosses placenta

IgE function

Parasites and allergic reactions

Antibody roles

Neutralization, opsonization, agglutination, complement activation, precipitation

Purpose of vaccination

Creates memory B/T cells without causing disease → rapid secondary response

Immune response to bacteria

Neutrophils, macrophages, complement, antibodies

Immune response to viruses

Interferons, NK cells, cytotoxic T cells, antibodies

Immune response to cancer

Cytotoxic T cells detect abnormal MHC I; NK cells destroy 'missing self' cells

Role of immune system in AIDS

HIV infects CD4 cells → decreased adaptive immunity → opportunistic infections

Self-reactive T/B cells

Normally eliminated (central tolerance); failure leads to autoimmunity