Disorders of the immune system (Condensed) 2026

The most important APCs for initiating T cell responses against protein antigens and is seen in epithelia and lymphoid organs

Dendritic cells

The "lymphocytes of innate immunity," which is responsible for antibody-dependent cellular cytotoxicity (ADCC)

NK cells

Type of lymphocyte responsible for direct killing of infected cells

Cytotoxic T cells

Type of lymphocyte responsible for producing cytokines to activate other leukocytes and stimulate B cells to become plasma cells

Helper T cells

Function of regulatory T cells

Suppress immune response

The CD8+ T cell recognizes which MHC class

MHC Class II

The CD4+ T cell recognizes which MHC class

MHC Class I - Expressed in all nucleated cells and platelets.

Systemic anaphylaxis, food allergies, bronchial asthma, and allergic rhinitis are examples of what type of hypersensitivity reaction; IgE-mediated/associated with allergies

Type I HSR

What is type II hypersensitivity reaction?

Antibody-mediated hypersensitivity

What is type III hypersensitivity reaction?

Immune-complex mediated hypersensitivity

Reactive arthritis, SLE, PSGN, polyarteritis nodosa, and serum sickness; and Arthus reactions are examples of what type of HSR

Type III HSR

What is type IV hypersensitivity reaction?

T-cell mediated hypersensitivity reaction. E.g., Tuberculin skin testing reactions

HLA type associated with ankylosing spondylitis and reactive arthritis

HLA-B27

HLA type associated with celiac disease (2)

HLA-DQ2, DQ8

HLA type associated with type I DM and multiple sclerosis (2)

HLA-DR, DQ

Specific autoantibody for SLE but has no correlation for disease activity

Anti-Sm (Smith)

Autoantibody specific for SLE and correlates with disease activity (i.e., nephritis)

Anti-dsDNA

Autoantibody associated with drug-induced lupus, such that implicated with hydralazine, procainamide, isoniazid, and penicillamine

Anti-histone

Autoantibody associated with neonatal lupus and congenital heart block and the most important autoantibodies in Sjögren syndrome (2)

Anti-Ro (SS-A), Anti-La (SS-B)

The two antiphospholipid antibodies present in antiphospholipid antibody syndrome (APAS)

Anti-cardiolipin, Anti-beta 2 glycoprotein I. Lupus anticoagulant can also cause prolonged aPTT

Type of endocarditis associated with SLE, with 1-3 mm warty deposits on heart valves, on either surface of the leaflets

Libman Sacks endocarditis

Targeted organs in Sjogren syndrome (2)

Lacrimal and salivary glands, Keratoconjunctivitis sicca for dry eyes and xerostomia for dry mouth

Isolated disorder of dry eyes and dry mouth

Sicca syndrome

Most common associated disease of Sjogren syndrome

Rheumatoid arthritis. Sjogren is associated with lymphomas as well.

Areas of body affected by limited scleroderma (3)

Fingers, forearm, and face

Components of CREST syndrome (5)

Calcinosis, Raynaud phenomenon, Esophageal dysmotility, Sclerodactyly, Telangiectasia

Autoantibody involved in CREST syndrome

Anti-centromere antibody

Most severely involved organ in scleroderma

Esophagus (rubber hose-like inflexibility of the lower 2/3 of the esophagus). This causes esophageal strictures and consequent dysphagia. In later stages, this can lead to atony at the lower end, causing GERD and increased risk for Barrett esophagus.

Major cause of death in systemic sclerosis

Pulmonary disease

Autoantibody in mixed connective tissue disease, which contains features that overlap with SLE, systemic sclerosis, and polymyositis

Anti U1 ribonucleoprotein (Anti-U1 RNP)

Defect found in selectin and integrins, associated with delayed separation of the umbilical cord and stump infection (omphalitis); autosomal recessive condition

Leukocyte adhesion deficiency

Primary immunodeficiency associated with impaired phagolysosome function, giant granules in leukocytes, albinism, and susceptibility to infection; autosomal recessive mutation of the LYST gene

Chediak Higashi syndrome

Enzyme deficient in chronic granulomatous disease

NADPH oxidase - This leads to inadequate superoxide needed for respiratory burst.

Chronic granulomatous disease is an X-linked recessive disease associated with susceptibility to infection with what type of organisms?

Catalase-positive organisms - Since they degrade hydrogen peroxide

Primary immunodeficiency associated with failure of B cell maturation due to defect in BTK gene, usually occurring in 6 months of age

Bruton Agammaglobulinemia

Gene impaired in ataxia-telangiectasia

ATM gene, Causes impaired DNA repair

Inherited/acquired disorder characterized by extracellular deposition of fibrillar protein, (+) apple green birefringence on polarized microscopy

Amyloidosis

What is the amyloid precursor in primary amyloidosis?

AL (amyloid light chain), Chiefly lambda type

What is the amyloid precursor in secondary amyloidosis, which is due to chronic inflammatory conditions?

AA (Amyloid A) - Serum amyloid A protein

What is the amyloid precursor in hemodialysis-associated amyloidosis?

Aβ2m: β2-microglobulin

Amyloid precursor in senile systemic amyloidosis

Transthyretin (TTR)

Most common and potentially most serious form of organ involvement in amyloidosis

Kidney - Thus the most common cause of death is renal failure as well.