Which cell adhesion receptors are Ca-independent?

The correct choice is immunoglobulin superfamily members, which include various receptors that mediate cell adhesion without the requirement for calcium ions. These cell adhesion molecules, found on the surface of cells, play critical roles in immune responses and other cellular interactions.

Unlike cadherins and selectins, which rely on calcium ions for their structural stability and functionality—cadherins require calcium for their adhesive properties to maintain connections between cells—immunoglobulin superfamily members function independently of calcium. Integrins can also operate without calcium, but they usually rely on the presence of divalent cations like magnesium or manganese to mediate their adhesive functions. Immunoglobulin superfamily members can form homophilic and heterophilic interactions without this dependency on calcium, providing versatility in cell signaling and adhesion processes.

This distinction emphasizes the unique properties of immunoglobulin superfamily members, making them particularly important in various biological contexts, especially in the immune system where such interactions are crucial for the adhesion and migration of immune cells.