Immune Pathology
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Direct answer
Immune pathology spans hypersensitivity reactions, autoimmune disease, vasculitis, immunodeficiency and transplant rejection. The Gell and Coombs classification anchors it: type I IgE immediate allergy, type II antibody-mediated cytotoxicity, type III immune-complex disease and type IV delayed T-cell hypersensitivity. FMGE repeatedly pairs an antibody or histological pattern with a disease — anti-dsDNA with lupus nephritis, anti-centromere with CREST, c-ANCA with granulomatosis with polyangiitis — so markers matter as much as clinical pictures.
What you must remember
- Hypersensitivity: type I — anaphylaxis, asthma, urticaria; type II — transfusion reactions, haemolytic disease of the newborn, Graves disease, Goodpasture syndrome; type III — serum sickness, lupus, post-streptococcal glomerulonephritis; type IV — tuberculin test, contact dermatitis, type 1 diabetes, graft rejection.
- SLE: young women with malar rash, arthritis and serositis; ANA sensitive, anti-dsDNA and anti-Smith specific; Libman-Sacks endocarditis and full-house glomerulonephritis; hydralazine and procainamide cause anti-histone-positive drug lupus.
- Rheumatoid arthritis: symmetric small-joint synovitis with pannus, anti-CCP more specific than rheumatoid factor, swan-neck deformity, subcutaneous nodules, Felty syndrome. Sjögren adds sicca with anti-Ro and anti-La.
- Systemic sclerosis: diffuse disease with anti-Scl-70; limited CREST (calcinosis, Raynaud, oesophageal dysmotility, sclerodactyly, telangiectasia) with anti-centromere.
- Vasculitis: giant cell arteritis after fifty with jaw claudication, high ESR and blindness risk needing urgent steroids; Takayasu (pulseless) in young women; polyarteritis nodosa with hepatitis B; IgA vasculitis with palpable purpura in children; c-ANCA (PR3) with granulomatosis with polyangiitis.
- Immunodeficiency: Bruton X-linked agammaglobulinaemia (boys after six months, absent tonsils and B cells); DiGeorge 22q11 with thymic aplasia and hypocalcaemia; severe combined immunodeficiency with early candidiasis and BCG dissemination; selective IgA deficiency, the commonest, causes anaphylactic transfusion reactions.
- Transplantation: hyperacute rejection in minutes from preformed antibody; acute rejection weeks to months, T-cell mediated; chronic rejection as graft arteriosclerosis; graft-versus-host disease affects skin, liver and gut after allogeneic marrow grafts.
Common confusion
Serum sickness (type III) appears one to two weeks after exposure with fever, urticaria and arthralgia, unlike minutes-onset IgE anaphylaxis. Anti-dsDNA tracks lupus activity while anti-Smith stays stable; c-ANCA pairs with granulomatosis with polyangiitis and p-ANCA with the other small-vessel vasculitides. In rejection timing, remember antibody causes hyperacute and T cells cause acute rejection.
Exam-focused takeaway
FMGE gives a vignette and expects one antibody or vasculitis name: malar rash with proteinuria (anti-dsDNA), temporal headache with visual loss (giant cell arteritis, steroids first), a boy with recurrent bacterial infections and absent immunoglobulins (Bruton). Hypersensitivity classification and rejection timing are near-guaranteed marks.
Frequently asked questions
Which antibody is most specific for SLE?
Anti-Smith; anti-dsDNA is also specific and correlates with nephritis and activity. ANA is the sensitive screen but not specific.
What is CREST syndrome?
Limited systemic sclerosis — calcinosis, Raynaud, oesophageal dysmotility, sclerodactyly and telangiectasia — with anti-centromere antibody. Diffuse disease with anti-Scl-70 is more aggressive.
How is graft rejection classified temporally?
Hyperacute within minutes to hours from preformed antibodies, acute within weeks to months from T cells, and chronic over months to years as vascular fibrosis. Each needs different prevention and treatment.
Which immunodeficiency follows 22q11 deletion?
DiGeorge syndrome with thymic aplasia, T-cell deficiency, hypocalcaemia from parathyroid aplasia and conotruncal heart defects — summarised as CATCH-22.
What type of hypersensitivity is the tuberculin reaction?
Type IV delayed hypersensitivity from sensitised CD4 cells recruiting macrophages, peaking at 48 to 72 hours; it underlies the Mantoux test.
Which vasculitis causes absent upper-limb pulses?
Takayasu arteritis of the aortic arch and branches in young women; giant cell arteritis is its counterpart after age fifty with temporal headache and jaw claudication.