Module 4: Occupational Asthma - Lecture (Continued)

5. PATHOPHYSIOLOGY:

5.1 Types of occupational allergens:

• complete antigens (e.g. grain, chemicals, animal products, metal salts);
• low molecular weight chemicals (e.g. isocyanates, acid anhydrides) = HAPTENS.

5.2 Method of action:

• Bind to body proteins which alter tertiary structure OR denature proteins (e.g. formaldehyde, glutaraldehyde).

• Antibody responses depend on type of allergen:

  1. Complete antigens e.g. flour-induced asthma: Type I hypersensitivity (IgE antibodies);
  2. Small molecular weight e.g. isocyanates - mechanism unknown.

5.3 Types of reactions:

(See the Figure)

1. Immediate: Max reaction (after 10-30 min); Recovery (within 1-2h);
2. Late - Early late: Max reaction (after 1-2h)
   Late late: Max reaction (after 4-8h);
3. Dual - Combination;
4. Atypical - progressive, square-waved, prolonged immediate.