Surfactant - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 793

13.3.3 Calcium

Calcium heightens phospholipid-protein aggregation, thereby reducing surfactant
viscosity [ 1559 ]. Calcium is required for the formation of tubular myelin by SPa, as
well as for agglutination, opsonization, and ligand binding of surfactant proteins.

13.4 Immune Function of Surfactant

Surfactant proteins belong to a class of C-type lectins, the collectins. Collectins
have 2 domains: (1) a carbohydrate-binding site at the surface of the mucosal layer
that can bind to various foreign substances (e.g., bacteria, viruses, fungi, molds,
and other allergens) and (2) a collagenous region underneath the mucous layer
that serves as a ligand for the collectin receptor on phagocytes and regulates C1q-
independent activation of the complement cascade.
Surfactant can activate macrophages. On the other hand, it hinders neutrophil
function [ 1559 ]. In addition, it operates as a prophagocytic and anti-inflammatory
material. Surfactant proteins have 2 immune functions: agglutination and opsoniza-
tion of foreign particles and pathogens.
Surfactant proteins stimulate, but surfactant lipids inhibit production of oxidants,
cytokines, and collagens and collagenases, NF B activity, and fibroblast prolifer-

ation. Decreased synthesis of pro-inflammatory cytokines and blocking of com-
plement activation associates with a shift from neutrophil activity to macrophage
phagocytosis.

κ

13.5 Governing Equations and Surfactant Transport

Modeling

Molecules in a fluid experience a mutual attraction. When the attractive force is
overcome by thermal agitation, molecules enter in the gazeaous phase. At a free
surface such as an air-water (gas-liquid) interface, water molecules in the bulk
fluid are surrounded by attractive molecules; at the interface, they are attracted
by a reduced number of molecules. As the surface has an energetic cost, fluid
minimizes its area. The surface tension ( T s ; with unit of force per unit length) is
a measure of energy loss per unit free surface area. Similarly, interfacial tension
at an immiscible liquid-liquid interface relies on different attractive intermolecular
forces in the 2 phases in contact.