Lecture on B Cells, T Cells, and the Immune System

Introduction

• B cells and T cells are part of the adaptive immune response.
• B Cells:
  • Part of the humoral immune response.
  • Produce antibodies to eliminate pathogens outside cells.
• T Cells:
  • Part of the cell-mediated immune response.
  • Cytotoxic T cells attack infected or abnormal cells (inside cells).
  • Prevent cancer cells from growing.

Major Histocompatibility Complex (MHC)

• Class 1 MHC:
  • Found on all nucleated human cells.
  • Communicates self-status to white blood cells.
  • Red blood cells do not have Class 1 MHC as they are not nucleated.
• Class 2 MHC:
  • Present on professional antigen-presenting cells (APCs).
  • Includes macrophages, dendritic cells, and B cells.
  • Liver cells and other non-APC cells have only Class 1 MHC.

Origins of B Cells and T Cells

• Both originate from hematopoietic stem cells in the bone marrow.
• B Cells:
  • Mature in the bone marrow.
  • Produce Ig molecules (pre-antibodies) on their surface.
  • Migrate to lymph nodes as naive B cells to screen for antigens.
• T Cells:
  • Differentiate in the thymus (hence the 'T' in T cells).
  • Have T cell receptors on their surface.
  • Migrate to lymph nodes with APCs to detect foreign antigens.

Structure and Function

• T Cells:
  • Have specific T cell receptors and MHC Class 1.
  • CD4 refers to T helper cells, CD8 to cytotoxic T cells.
• B Cells:
  • Have B cell receptors and MHC Class 1 and 2 (as APCs).

Clonal Selection

• Process:
  • Generation of billions of different receptors on B and T cells.
  • Removal of cells that bind to self-antigens (immune tolerance).
  • Naive B and T cells with diverse receptors reside in lymph nodes.
• Activation:
  • Occurs when an antigen binds specifically to a receptor.
  • Leads to clonal expansion, producing millions of immune cells.
  • Cells produce antibodies or become active cytotoxic T cells.

Conclusion

• Clonal selection is crucial for adaptive immunity.
• Active lymphocytes circulate to combat specific pathogens.
• Next topic will cover the role of T helper cells in the immune system.