Which type of cell adhesion receptor is not Ca2+ dependent?

Immunoglobulins are a type of cell adhesion receptor that do not require calcium ions (Ca2+) for their adhesive properties. Unlike selectins and cadherins, which rely on the presence of calcium to maintain their structural integrity and mediate cell-cell adhesion, immunoglobulins interact through specific protein-protein interactions that are not influenced by calcium concentrations.

Integrins, while they play a crucial role in cell adhesion to the extracellular matrix and cell signaling, also have a different mechanism involving cation binding, but not specifically requiring calcium for their function in adhesion. Therefore, the unique characteristic of immunoglobulins lies in their ability to facilitate adhesion independently of calcium, differentiating them from the other receptors listed.