21.4 Lymphocytes and Antigen-Presenting Cells

Two types of lymphocytes

• B lymphocytes (B cells)—humoral immunity

• T lymphocytes (T cells)—cellular immunity

• Antigen-presenting cells (APCs) -

• Do not respond to specific antigens

• Play essential roles in immunity

origin of lyphocytes

: both lymphocytes originate in red bone marrow

Immunocompetence:

• lymphocytes must be able to recognize only 1 specific antigen

  • B or T cells display only one unique type of antigen receptor on surface when mature so bind only one specific antigen

Self-tolerance

: lymphocytes must be unresponsive to own antigens

Seeding secondary lymphoid organs and circulation

• Immunocompetent B and T cells not yet exposed to antigen are called naive

• Exported from primary lymphoid organs (bone marrow and thymus) to colonize secondary lymphoid organs (lymph nodes, spleen, etc.)

1. Antigen encounter and activation

• Naive lymphocyte’s first encounter with antigen triggers lymphocyte to develop further

• Lymphocyte is selected to differentiate into active cells by binding to its specific antigen: AKA clonal selection

1. Proliferation and differentiation

• make clones or copies of itselv

• -next time, boy will be prepeared for next flu season

• Antigen receptor diversity: 

• Genes, not antigens, determine which foreign 

Antigen- Presenting Cells (APC’s):

Engulf antigens and present fragments of antigens to T cells for recognition

majpr types of anigen presenting cells (APC’s) -

dendrite cells

macrophages

B cells

moving around and cleaning up