Key Summary of Pulmonary Surfactant Associated Protein A (SP-A):

Molecular Structure: SP-A is a collectin protein comprising an octadecamer with six trimeric subunits. It has a collagen-like section and carbohydrate recognition domain (CRD), encoded by two genes (SFTPA1 and SFTPA2).

Lung Function: Critical for maintaining alveolar surface tension, preventing lung collapse during exhalation. Manages surfactant metabolism, phospholipid interactions, and controls surfactant release from type II alveolar cells.

Immune Defence: Recognizes and binds to pathogens like bacteria, viruses, and fungi. Enhances macrophage pathogen elimination, controls inflammatory responses, and links innate and adaptive immunity.

Disease Implications: Variations in SP-A are associated with respiratory conditions like infant respiratory distress syndrome, asthma, COPD, and lung fibrosis. External factors like smoking can alter its function.