This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology and Rheumatology, Subject name: Medicine
Caplan's syndrome of rheumatoid arthritis with pneumoconiosis is characterized by 
Select and explain. 
A. Lung nodules and diffuse pulmonary fibrosis, B. Bilateral symmetrical lung cavitations with pulmonary fibrosis., C. Air-space consolidation with patchy pulmonary fibrosis., D. Interstitial pneumonitis with hilar adenopathy.
A: Lung nodules and diffuse pulmonary fibrosis
Answer: A: Lung nodules and diffuse pulmonary fibrosis 
Explanation: Ans. a (Lung nodules and diffuse pulmonary fibrosis). (Ref. Harrison, Medicine, 16th ed., 1524)CAPLAN'S SYNDROME# Caplan's syndrome is characterized by triad of- Pulmonary nodules,- Pneumoconiosis (progressive massive fibrosis), and/in- Rheumatoid disease (seropositive).# The immuno-pathological mechanism involves:- Direct cytotoxicity of inorganic dust- Stimulation of reactive oxygen- Activation of macrophages to produce cytokines and TNF alpha (fibrogenic factor)- Increased protease activity- Increased activation of alpha 1 antitrypsin and leucocyte elastase activity.