Chapter 3: Inflammation Pathology

Acute inflammation is defined as an immediate reaction to tissue damage or infection, characterized by the cardinal signs of redness, heat, swelling, pain, and loss of function. These physical manifestations result from significant hemodynamic changes, including massive vasodilation and increased vascular permeability triggered by chemical messengers like histamine, bradykinin, and prostaglandins. The primary cellular participants are neutrophils, which undergo a highly regulated journey from the bloodstream to the injury site involving margination, rolling facilitated by selectins, and firm adhesion mediated by integrins. Once they exit the vasculature through diapedesis, these cells follow chemotactic signals such as leukotriene B4 and complement factor C5a to locate pathogens. The process of phagocytosis is enhanced by opsonins like IgG and C3b, leading to the destruction of microbes via oxygen-dependent respiratory bursts or oxygen-independent enzymatic activity. Clinical pathologies such as leukocyte adhesion deficiency, Chediak-Higashi syndrome, and chronic granulomatous disease are discussed as examples of how genetic defects in these pathways compromise the immune response. The text further explores chronic inflammation, a prolonged state involving macrophages, lymphocytes, and eosinophils, often triggered by persistent infections or autoimmune disorders. A specialized form of this is granulomatous inflammation, where modified macrophages transform into epithelioid cells and multinucleated giant cells to wall off persistent threats like tuberculosis or fungal pathogens. Finally, the chapter categorizes diverse tissue-level responses to infection, ranging from neutrophil-rich exudative patterns and tissue-destroying necrotizing inflammation to the diffuse interstitial infiltrates typical of viral infections and the specific cellular changes seen in cytopathic reactions.