Cell Adhesion Molecules (CAMs) – Lymphocyte Recirculation and Homing

00:01 What are cell adhesion molecules? Well they have adhesion molecules that are present on the surface of cells that recognize other molecules in the body.

00:10 And sometimes these cell adhesion molecules or CAMs as we often call them, will promote cell-cell and cell-extracellular matrix interactions.

00:21 So it may be that the molecule they recognize is on the surface of another cell or it may be that the molecule they recognize is part of the extracellular matrix.

00:31 They can be expressed constitutively, in other words they’re already there, or they can be induced by pathogens and host products during inflammation.

00:41 So following encounter with a pathogen or some host substance, you might induce expression of the gene for an adhesion molecule.

00:50 And an adhesion molecule that wasn’t there previously now becomes expressed on the cell surface.

00:56 Sometimes adhesion molecules recognize the same adhesion molecule on another cell, in other words homophilic interactions. But alternatively, an adhesion molecule may recognize a different adhesion molecule on another cell, heterophilic interaction.

01:16 There are five main groups of cell adhesion molecules: The cadherins, the immunoglobulin-superfamily cell adhesion molecules, mucin-like cell adhesion molecules, group of adhesion molecules called selectins and another quite large family called the integrins.

01:43 Integrins are interesting because they can signal in two different ways.

01:48 They are often present on the membrane of the cell in a particular conformation, or the way that they’re folded, which means that they are a very low affinity for the ligands that they recognize and therefore are essentially inactive.

02:08 However, signaling from within the cell involving the molecule talin interacting with the actin network within the cell, can lead to what is called inside-out signaling.

02:21 So the signal here is being initiated from within the cell.

02:26 And that signal, being delivered through talin allows a change in the conformation, so that now you have a high affinity active conformation.

02:37 And as you can see here these integrins are heterodimers, they consist of two chains, an alpha (α) chain and a beta (β) chain.

02:45 And now, following this change in conformation, the integrin is able to interact with cell or extracellular matrix adhesion molecules.

02:57 In contrast to inside-out signaling, integrins can also interact in a way that is perhaps more typical when we think of signaling.

03:07 They can interact with an external ligand, in other words outside-in signaling.

03:14 And in this situation, what happens is that ligands lead to a cross linking of several integrin heterodimers and molecules such as the kinase Src and the molecule FAK are involved in this process.

03:30 And you get a clustering of several integrin heterodimers together.

03:36 So there are multiple copies, that’s what the end there is representing - multiple copies of the integrins clustered together. And this can lead to cell polarity changes, to survival and migration of the cells, due to changes in the cytoskeleton and gene expression.