Skin testing in farmers' lung disease

Area of Science:

• Immunology
• Pulmonary Medicine
• Occupational Health

Background:

• Farmers' lung disease (FLD) is a hypersensitivity pneumonitis.
• Micropolyspora faeni is a known causative agent.
• The immunological mechanisms underlying FLD are not fully understood.

Purpose of the Study:

• To investigate the role of immediate and late-onset skin test reactions to Micropolyspora faeni in FLD.
• To identify the immunological factors responsible for skin sensitization in FLD patients and exposed farmers.

Main Methods:

• Intradermal skin testing with M. faeni antigen in FLD patients and control farmers.
• Prausnitz-Küstner (P-K) reactions and radioimmunoassay to detect specific IgE.
• Fractionation of patient serum using staphylococcal protein A-Sepharose.
• Biopsy of late-onset skin reactions for histological examination.

Main Results:

• 75% of FLD patients and 79% of antibody-positive farmers showed immediate skin test reactions.
• A skin-sensitizing factor was found in the IgG-rich fraction of serum from positive reactors.
• M. faeni-specific IgE was not detected.
• Late-onset skin reactions occurred only in FLD patients and farmers with precipitating antibodies, showing inflammatory infiltrates and immune complex deposition.

Conclusions:

• Immediate skin test reactivity to M. faeni is common in FLD patients and seropositive farmers.
• A non-disease-specific, IgG-associated skin-sensitizing factor is present in affected individuals.
• The precise role of this IgG factor in FLD pathogenesis requires further investigation.