How is the pathogenesis of HP?

Occurs with exposure to correct size and composition dusts (0.5-5 mcm, antigenic, resistant to degradation and persists long enough in lung tissues for sensitization) Pt must be senstized during a pervious exposure, sensitization durationis variable (months to years), not all subjects get sensitized. Proinflammatory cytokines (IFN-gamma, IL10, TNF) activated macrophages, CD8 lymphocytes and form granuloma promoting fibrosis Type III and IV (and some I and II) hypersensitivty caused lung injury followed by T cell mediated hypersensitivity, inflammation, granuloma formation, fibrosis.