B Cells and T Cells

• Role in Immune Function
  • Both B cells and T cells are white blood cells.
  • They have a protective role in fighting infections.
  • Originate from hematopoietic stem cells in the bone marrow.

B Cells

• Function

  • Main function: recognition of antigens.
  • Made in the bone marrow, travel via bloodstream to organs like the spleen and lymph nodes.

• B Cell Receptors

  • Located on the surface of B cells.
  • Bind to antigens (foreign substances like harmful bacteria/pathogens).

• Process after Antigen Binding

  • Antigen is engulfed by B cell (receptor-mediated endocytosis).
  • Breakdown products are presented on the B cell surface via Major Histocompatibility Complex (MHC) class II.

• Interaction with Helper T Cells (CD4 Lymphocytes)

  • Helper T cells recognize and bind to MHC class II.
  • Release lymphokines:
    • Causes B cell to clone itself (mitosis).
    • Differentiation into plasma cells.

• Plasma Cells

  • Produce antibodies specific to the antigen initially bound.

T Cells

• Helper T Cells (CD4 T Cells)

  • Bind to MHC class II on B cells.
  • Release lymphokines upon binding.

• Cytotoxic T Cells (CD8 T Cells)

  • Function: attack cells infected by viruses.
  • Recognize viral proteins presented by infected cells via MHC class I.

• Response to Infected Cells

  • Bind to abnormal peptides on infected cells.
  • Secrete cytotoxins (e.g., perforin, granulysin) to initiate apoptosis.
  • Express FAS ligand to bind with FAS on infected cells and form a death-inducing signaling complex.

• Memory T Cells

  • Replicate quickly and respond rapidly if encountered the antigen before.

Adaptive Immunity

• Both B and T cells are part of the body's adaptive immunity.
• Specialized network of cells specifically responding to pathogens and fighting infections.