JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD Pharm. D II Year PATHOPHYSIOLOGY Previous Question Paper (August/September - 2022 - R08)

Hypersensitivity reactions are exaggerated or inappropriate immune responses to antigens, classified into four types by Gell and Coombs:

• Type I (Immediate): IgE-mediated, involving mast cell degranulation and histamine release (e.g., anaphylaxis, asthma).
• Type II (Cytotoxic): IgG or IgM antibodies bind to antigens on cell surfaces, leading to cell destruction via complement activation or antibody-dependent cellular cytotoxicity (ADCC). Examples include transfusion reactions and hemolytic disease of the newborn.
• Type III (Immune Complex): Antigen-antibody complexes deposit in tissues, triggering inflammation and neutrophil recruitment (e.g., systemic lupus erythematosus).
• Type IV (Delayed-type): Cell-mediated response involving sensitized T-lymphocytes and macrophages, occurring 24-72 hours after exposure (e.g., contact dermatitis, tuberculin skin test).

In Type II reactions, the immune system mistakenly targets endogenous or exogenous antigens on host cells. The binding of antibodies activates the complement system, creating the membrane attack complex (MAC) which causes cell lysis, or promotes phagocytosis by opsonization. In Type IV reactions, there is no antibody involvement. Instead, antigen-presenting cells activate T-cells, which release cytokines that recruit macrophages and inflammatory cells, resulting in tissue damage at the site of antigen contact.

Radiation causes biological damage primarily through the ionization of water molecules in cells, producing highly reactive free radicals such as hydroxyl radicals. These free radicals induce damage to cellular components, most critically DNA.

Key biological effects include:

• DNA Damage: Single or double-strand breaks can lead to mutations, chromosomal aberrations, or cell death if the damage is irreparable.
• Cell Cycle Arrest: Cells may stop dividing to attempt repair; if the damage is too severe, the cell undergoes apoptosis.
• Tissue Effects: Rapidly dividing tissues (bone marrow, gastrointestinal epithelium, gonads) are most sensitive, leading to symptoms like anemia, immunosuppression, and gastrointestinal distress.
• Carcinogenesis: Long-term effects include the potential for malignant transformation due to accumulated genetic mutations.