MODULE 6

Autoimmunity

Immune system attacks the body’s own cells due to loss of self-tolerance.

Causes of Autoimmunity

Loss of tolerance, autoantibodies, autoreactive T cells, genetic and environmental factors.

Sequestered Antigens

Hidden tissues (eye, brain) exposed to immune system → attack.

Forbidden Clones

Self-reactive lymphocytes escape destruction during development.

Immune Evolution

Mutations make immune cells reactive to self.

Molecular Mimicry

Microbes mimic self-antigens → mistaken immune attack.

Tissue Damage in Autoimmunity

Inflammation exposes self-antigens → further immune attack.

Mnemonic for Autoimmunity Origins

Silly Frogs Imitate My Tissues → Sequestered, Forbidden, Immune evolution, Mimicry, Tissue damage.

Systemic Autoimmunity

Affects multiple organs; involves immune complexes and inflammation.

Systemic Lupus Erythematosus (SLE)

Autoantibodies to DNA, mitochondria, cell parts → inflammation in skin, joints, kidney, heart.

Rheumatoid Arthritis (RA)

Autoantibodies (IgM vs IgG) deposit in joints → chronic inflammation and tissue damage.

Endocrine Autoimmunity

Autoimmunity targeting endocrine glands (thyroid, pancreas).

Graves’ Disease

Antibodies overstimulate thyroid → excess thyroxine → hyperthyroidism.

Hashimoto’s Thyroiditis

Antibodies destroy thyroid tissue → low thyroxine → hypothyroidism.

Type 1 Diabetes Mellitus

T cells and antibodies destroy pancreatic beta cells → loss of insulin.

Neuromuscular Autoimmunity

Autoimmunity affecting muscles or nerves.

Myasthenia Gravis

Autoantibodies block acetylcholine receptors → muscle weakness.

Multiple Sclerosis (MS)

T cells and antibodies destroy myelin → nerve damage and paralysis.

Mnemonic for Neuromuscular Autoimmunity

My Muscles Suffer → Myasthenia + Multiple Sclerosis cause muscle issues.

Immunodeficiency Diseases

Failure or loss of part of the immune system.

Primary Immunodeficiency

Genetic; present at birth (SCID, DiGeorge).

Secondary Immunodeficiency

Acquired; from infection, cancer, drugs, stress, or aging.

B-cell Defects

Agammaglobulinemia (no antibodies), Hypogammaglobulinemia (low antibodies), Selective Ig deficiency (missing one type).

T-cell Defects

DiGeorge Syndrome (no thymus, no T cells), Chronic Candidiasis (persistent fungal infections).

Combined B and T Defects

SCID (no adaptive immunity), ADA deficiency (no lymphocyte survival), Wiskott-Aldrich, Ataxia-Telangiectasia.

Phagocyte Defects

Chediak-Higashi (poor phagocytosis), Chronic Granulomatous Disease (no killing ability), adhesion defects.

Complement Defects

C deficiencies cause recurrent infections; hereditary angioedema causes swelling; autoimmune overlap possible.

Secondary Immunodeficiency Causes

Natural (infection, cancer, stress, malnutrition, aging); Artificial (chemo, steroids, transplant drugs, spleen removal).

Mnemonic for Secondary Immunodeficiency

I CAN STARVE → Infection, Cancer, Aging, Nutrition, Stress, Therapy, Autoimmune, Removal (spleen), Viruses, Environment.

Immune System and Cancer

Immune system normally kills abnormal cells; failure → tumor growth.

Tumor Types

Benign = localized; Malignant = spreading and aggressive.

Cancer Causes

Gene mutation, oncogenes, retroviruses, mitosis errors.

Immune Surveillance

Immune system detects and destroys abnormal cells.

Failure of Immune Surveillance

Allows tumor growth and cancer progression.

Organ Transplantation

Replacing diseased organ with donor tissue; immune system may attack due to foreign MHC.

Transplant Problem

Recipient’s immune system recognizes donor tissue as foreign and attacks.

Transplant Solution

Match MHC closely and use immunosuppressive drugs.

Types of Transplants

Autograft (self), Isograft (identical twin), Allograft (same species), Xenograft (different species).

Mnemonic for Transplants

AIX → Auto, Iso, Xeno.

Host vs Graft Reaction

Recipient T cells attack donor organ → rejection.

Graft vs Host Reaction

Donor immune cells attack recipient tissues.

Mechanism of Transplant Rejection

Recipient T cells recognize donor MHC → release IL-2 → activate cytotoxic T cells → tissue damage.

Summary Table of Immune Disorders

Type I = Allergy (IgE), Type II = Cytotoxic (IgG + complement), Type III = Immune Complex (IgG deposits), Type IV = Delayed (T-cell), Autoimmunity = Self-attack, Immunodeficiency = Immune loss, Transplant = MHC mismatch.

Final Mnemonic for Disorders

ACID Auto Defends Transplants → Allergy, Cytotoxic, Immune Complex, Delayed, Autoimmunity, Deficiency, Transplant.