Lymphocytes and Langerhans cells in patch tests. An immunohistochemical and electron microscopic study

Area of Science:

• Immunodermatology
• Cellular immunology
• Electron microscopy

Background:

• Patch testing is crucial for diagnosing allergic contact dermatitis.
• Differentiating allergic from irritant reactions can be difficult clinically.
• Immunohistopathology and electron microscopy offer insights into cellular responses.

Purpose of the Study:

• To compare the distribution of immunocompetent cells in allergic (nickel) and irritant (dithranol) patch tests.
• To evaluate the utility of transmission electron microscopy and monoclonal antibody labelling in differentiating these reactions.

Main Methods:

• Biopsies from patch tests were analyzed 24-48 hours post-application.
• Conventional transmission electron microscopy was employed.
• Avidin-biotin immunoperoxidase staining with monoclonal antibodies (OKT11, OKT4, OKT8, NK9, OKT6, OKIal) was performed.

Main Results:

• Both allergic and irritant reactions showed a predominance of pan T lymphocytes (OKT11+), primarily helper/inducer (OKT4+) and a minority of suppressor/cytotoxic (OKT8+) cells.
• Natural killer cells (NK9+) were present in low numbers.
• Langerhans cells (OKT6+, OKIal+) showed no change in allergic reactions but an increase in OKIal+ cells in irritant reactions.
• Dithranol caused significant mitochondrial changes in Langerhans cells, unlike keratinocytes.

Conclusions:

• Current immunohistopathological and electron microscopic techniques cannot reliably differentiate between allergic and irritant patch tests.
• Minor differences in cellular infiltration and Langerhans cell morphology were observed but were insufficient for definitive distinction.