Immunopathology

Immunopathology

Fab region
Fc portion
Immunoglobulin structure

Type I hypersensitivity reaction

chronic inflammation due to type I hypersensitivity reaction: Nasal mass with edematous stroma with chronic inflammatory cell infiltrate ( mainly eosinophils) covered by ciliated columnar epitheliumallergic nasal polyp


Bronchial asthma is an example of type I hypersensitivity reaction & is characterized by eosinophilic infiltrate, mucus collection & congestion.


Antibody –mediated (type II) hypersensitivity Is mediated by antibodies directed against target antigens that are fixed on the surface of cells by one of the following mechanisms

Type III hypersensitivity ( Immune complex-mediated)Is mediated by deposition of antigen-antibody (immune) complexes followed by complement activation and accumulation of polymorph nuclear leukocytes.


The deposition of immune complexes in an artery is called vasculitis with circumferential bright pink area of fibrinoid necrosis with protein infiltration & inflammation


Cell mediated (type IV) hypersensitivity : the antigen presented by dendritic cell ( antigen presenting cell) leads to activation of TH1 cell which secrete cytokines that activate macrophages to form epithelioid cells & granuloma.

The granuloma is composed of localized collection of epithelioid cells surrounded by lymphocytes with langhans type giant cell.

It is a complex immunologic phenomenon involving both cell & Ab mediated hypersensitivity responses of the host directed against histocompatibility molecules on the donor allograft

Hyper acute rejection of a kidney allograft showing endothelial vascular damage (by preformed antibodies) with formation of fibrin-platelet thrombi in the glomerular capillaries.


This is a form of acute renal transplant rejection known as acute cellular tubulointerstitial rejection because most of the inflammation is in the interstitium. The glomerulus seen here is normal, but the tubules are infiltrated by many lymphocytes at the upper right

The renal arteries with chronic vascular rejection are markedly thickened with intimal fibrosis (arrow). There is interstitial fibrosis and chronic inflammation. Such chronic rejection usually occurs slowly over several months to years following transplantation. This disease, unlike acute rejection, is difficult to treat.

salivary glands characteristically show dense lymphocytic infiltration.

Kaposi sarcoma : atypical spindle cells enclosing slit like vascular spaces this otherwise rare tumour is a frequent finding in patient with AIDS.

opportunistic infections in AIDS

This is cytomegalovirus (CMV) infection in the lung. Note the very large cells that have large violet intranuclear inclusions with a small clear halo. Basophilic stippling can be seen in the cytoplasm.
"Three M’s of herpes simplex virus" - margination of nuclei, molding and multi nucleationWith intranuclear eosinophilic amorphous or droplet - like bodies surrounded by a clear halo

Pneumocystis jiroveci

is a fungus that only causes disease in immunosuppressed patients due to HIV infection or transplantation. It spreads by droplet infection leading to pneumonia. Microscopically, the typical case is characterized by a foamy or honeycombed intra-alveolar exudate accompanied by a lymphoplasmacytic interstitial infiltrate preventing gas exchange.

Cerebral toxoplasmosis with hemorrhagic necrotic lesion compressing brain tissue

Amyloidosis

Macroscopically the affected organ(lymph node ) is enlarged, firm & has waxy consistency

By H&E the amyloid appears as an amprphous, eosinophilic hyaline extracellular substance that with progressive accumulation lead to pressure atrophy of adjacent cells


A section of liver stained with congo red reveals pink-red deposits of amyloid in the wall of blood vessels & along the sinusoids
Note the yellow green birefringence of the deposits when observed by polarizing microscope