Cell Adhesion Mechanisms and Molecules

Cell Adhesion

• A variety of cell adhesion mechanisms organize cells in tissues.
• Stable cell interactions maintain tissue structural integrity.
• Cell adhesion is crucial for normal embryonic development, tissue organization, immune responses, and wound healing.
• Cell adhesion is mediated by cell-matrix adhesions (cells to extracellular matrix) and cell-cell adhesions.
• In multicellular organisms, cells adhere directly or via the extracellular matrix (ECM).

Types of Cell Adhesion Molecules (CAMs)

• CAMs are broadly classified into integrins, cadherins, selectins, and immunoglobulin-like CAMs (IgCAMs).
  • Integrins:
    • Principal receptors for cells to bind to the extracellular matrix.
    • Function as signal transducers, activating intracellular signaling pathways.
    • Cooperate with conventional receptors for cell growth, survival, and proliferation.
  • Cadherins:
    • Transmembrane proteins mediating cell-cell adhesion in animals.
    • Crucial for tissue morphogenesis and homeostasis.
    • Control cell-cell adhesion and cell signaling.
    • Implicated in germ cell positioning and migration.
    • Mediate signals controlling cell fate specification, cell polarity, and proliferation.
  • Selectins:
    • Vascular cell adhesion molecules involved in adhesive interactions of platelets, leukocytes, and endothelial cells.
    • First step of a cascade of molecular interactions leading to leukocyte extravasation.
    • Enable lymphocyte recirculation and leukocyte migration.
    • Bind to carbohydrate structures on glycoproteins, glycolipids, and proteoglycans.

Immunoglobulin-like CAMs (IgCAMs)

• ICAM-1 is a cell surface glycoprotein and adhesion receptor.
• Expressed at low basal levels in immune, endothelial, and epithelial cells.
• Up-regulated in response to inflammatory stimulation.
• Regulates leukocyte recruitment from circulation to sites of inflammation.
• A master regulator of tissue functions during onset/resolution of pathologic conditions.

Immunoglobulins

• Immunoglobulins act as cell-surface receptors for antigens, enabling cell signaling and activation.
• Also act as soluble effector molecules neutralizing antigens.
• IgG:
  • Most common antibody type in blood (75%).
  • Prevents infections and attacks foreign substances.
  • Crosses the placenta, entering the developing fetus.
• IgA:
  • Protects mucosal tissues (respiratory, gastrointestinal, genitourinary tracts) from microbial invasion.
  • Most abundant antibody in the body.
  • Secreted in saliva, tears, and breast milk.
• IgD:
  • Plays a role in the immune system, but exact functions are not fully understood.
• IgE:
  • Antibodies produced by the immune system in response to allergens.
  • Travel to cells that release chemicals causing allergic reactions.
  • Bind to parasites like worms and protozoa to destroy them.
• IgM:
  • Body's first line of defense against new infections, providing short-term protection.
  • IgM levels increase after exposure, then decrease as the body produces other antibodies.
  • Largest antibody isotype in vertebrates.

Explore the vital mechanisms of cell adhesion that are crucial for tissue integrity and development. This quiz covers various types of cell adhesion molecules, including integrins and cadherins, and their roles in processes such as immune responses and wound healing.