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Hypersensitivity Reactions: Immune-Complex Reactions

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Type III hypersensitivity reactions occur when antigen–antibody complexes form and activate the complement system. Normally, these complexes help the clearance of antigens by phagocytes and red blood cells. However, when large numbers of immune complexes are present, they can deposit in tissues—particularly in the walls of blood vessels—leading to inflammation and tissue injury. These deposits trigger complement activation and neutrophil recruitment, resulting in serum sickness, a systemic...

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Delayed-Type Hypersensitivity (DTH), or Type IV hypersensitivity, is a cell-mediated immune response. It occurs when T cells, rather than antibodies, mediate a reaction to specific antigens. It is characterized by a delayed onset (1-2 days) and involves the recruitment of macrophages to the inflammation site.The initiation of a DTH response begins with the sensitization of T cells. During this phase, which lasts at least 1-2 weeks, antigen-specific T cells are activated, clonally expanded, and...

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Type II hypersensitivity involves IgG and IgM antibodies targeting cell surface antigens, leading to cell destruction. This can occur through complement activation, antibody-dependent cell-mediated cytotoxicity (ADCC), or acting as opsonins for phagocytosis. When excessive, these reactions cause significant tissue damage.Drug-induced hemolytic anemia is a common example, where drugs like penicillin or cephalosporins bind to red blood cells, forming drug-protein complexes. These complexes...

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Updated: Jul 13, 2026

Recognition of Epidermal Transglutaminase by IgA and Tissue Transglutaminase 2 Antibodies in a Rare Case of Rhesus Dermatitis

Recognition of Epidermal Transglutaminase by IgA and Tissue Transglutaminase 2 Antibodies in a Rare Case of Rhesus Dermatitis

Published on: December 15, 2011

Histoid leprosy with ENL reaction.

Suresh K Sharma¹, Namita Rath, R K Gautam

¹Department of Skin and STD, Dr RML Hospital, New Delhi-110 001, India.

Indian Journal of Dermatology, Venereology and Leprology

|July 28, 2007

Summary

Histoid leprosy can manifest with firm nodules that may suppurate during multidrug therapy (MDT). These nodules can exhibit erythema nodosum leprosum (ENL), a rare but significant finding in this leprosy form.

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Recognition of Epidermal Transglutaminase by IgA and Tissue Transglutaminase 2 Antibodies in a Rare Case of Rhesus Dermatitis

Recognition of Epidermal Transglutaminase by IgA and Tissue Transglutaminase 2 Antibodies in a Rare Case of Rhesus Dermatitis

Published on: December 15, 2011

Contact Hypersensitivity as a Murine Model of Allergic Contact Dermatitis

Contact Hypersensitivity as a Murine Model of Allergic Contact Dermatitis

Published on: September 26, 2022

Area of Science:

Dermatology
Infectious Diseases
Pathology

Background:

Histoid leprosy is a rare form of Mycobacterium leprae infection.
Cutaneous and subcutaneous nodules are characteristic manifestations.
Multidrug therapy (MDT) is the standard treatment.

Purpose of the Study:

To report a case of histoid leprosy with unusual erythema nodosum leprosum (ENL) development.
To highlight the histopathological features of ENL in this context.

Main Methods:

Clinical presentation of a 23-year-old male patient with histoid leprosy.
Observation of nodule suppuration during MDT.
Histopathological examination of suppurated nodules.

Main Results:

The patient presented with firm cutaneous and subcutaneous nodules.
Some nodules suppurated following initiation of MDT.
Histopathology confirmed erythema nodosum leprosum (ENL) in the suppurated nodules.

Conclusions:

Erythema nodosum leprosum (ENL) can occur in histoid leprosy, even after the initiation of MDT.
This case underscores the importance of histopathological examination for diagnosing rare leprosy complications.