Functional human epidermal Langerhans cells that lack Birbeck granules

Area of Science:

• Immunology
• Cell Biology
• Dermatology

Background:

• Birbeck granules (BG) are unique cytoplasmic organelles found in Langerhans cells (LC).
• The precise function of BG in LC remains incompletely understood, with proposed roles in endocytosis and antigen presentation.
• Previous research suggested BG are integral to LC function.

Purpose of the Study:

• To investigate the role of Birbeck granules (BG) in Langerhans cell (LC) function.
• To determine if the absence of BG impacts the antigen-presenting capacity of LC in vivo and in vitro.

Main Methods:

• Electron microscopy was used to examine skin biopsy specimens from a healthy individual over 2.5 years.
• Immunohistochemistry with a BG-specific monoclonal antibody confirmed the absence of BG.
• LC morphology, number, and expression of CD1a and HLA class II were assessed.
• Functional assessment included hapten sensitization (diphenylcyclopropenone) and allogeneic mixed epidermal cell-lymphocyte reaction (mELR).

Main Results:

• A healthy adult was identified with Langerhans cells (LC) completely lacking Birbeck granules (BG) across multiple skin sites and over time.
• These BG-negative LC maintained normal morphology, cell counts, and expression of CD1a and HLA class II.
• The individual exhibited normal sensitization to diphenylcyclopropenone with increased HLA class II expression on LC, indicating activation.
• Epidermal cells from the individual showed normal function in an allogeneic mixed epidermal cell-lymphocyte reaction.

Conclusions:

• The complete absence of Birbeck granules (BG) does not impair the presence, morphology, or basic immunophenotype of Langerhans cells (LC).
• BG-negative LC retain normal antigen-presenting capabilities, as evidenced by in vivo sensitization and in vitro mixed epidermal cell-lymphocyte reaction.
• These findings strongly suggest that Birbeck granules (BG) are not a prerequisite for normal Langerhans cell (LC) function.