31. Which one of the following statements about cell-cell interactions is NOT true?
A. Cadherins are transmembrane linker proteins which carry out Ca²⁺-mediated adhesion between adjacent cells.
B. Integrins are transmembrane adhesion proteins that mediate hemophilic adhesion through actin and intermediate filaments.
C. Selectins are cell surface lectins that mediate a variety of transient, cell-cell adhesion interactions in the bloodstream.
D. ICAMs (intracellular cell adhesion molecules) and VCAMs (vascular cell adhesion
molecules) are members of immunoglobulin (lg) superfamily
(1) only A                                              (2) only B
(3) Both C and D                                    (4) Both A and D

The statement that is NOT true about cell-cell interactions is:

(2) only B

Explanation:

• A is true: Cadherins are transmembrane linker proteins that mediate calcium (Ca2+)-dependent homophilic adhesion between adjacent cells. This adhesion is important for tissue integrity and adherens junction formation.​

• B is false: Integrins are transmembrane adhesion proteins, but they primarily mediate heterophilic adhesion mostly between cells and the extracellular matrix (ECM), not hemophilic adhesion (i.e., between identical molecules on adjacent cells). Integrins also link to actin cytoskeleton but not intermediate filaments directly.​

• C is true: Selectins are cell surface lectins that mediate transient, carbohydrate-dependent cell-cell adhesion interactions in the bloodstream, playing a key role in leukocyte rolling and homing during inflammation.​

• D is true: ICAMs (intracellular adhesion molecules) and VCAMs (vascular cell adhesion molecules) belong to the immunoglobulin (Ig) superfamily and mediate important cell-cell adhesion interactions, especially in immune cell trafficking.​

Summary

Conclusion

The incorrect statement is B: integrins primarily function in cell-ECM adhesion and do not mediate hemophilic cell-cell adhesion, which is a characteristic of cadherins. Statements A, C, and D accurately describe their respective adhesion molecules.