Cells and Organs of the Immune System Cells

Cells and Organs of the Immune System Cells – Leukocytes a. Lymphocytes – specialized for adaptive immunity b. Granulocytes/Agranulocytes – func in accessory roles in adaptive immunity Immune Organs – 2 major groups a. 1° lymphoid organs – where lymphocytes dev. and mature b. 2° lymphoid organs – where lympho’s interact w/ Ag

Hematopoiesis • Begins with hematopoietic stem cells (HSC) – Few in # in bone marrow; difficult to culture – Pluripotent; able to produce RBC’s, WBC’s, megakaryocytes • HSC differentiates to become: either a) Myeloid progenitor cell or b) Lymphoid progenitor cell Myeloid RBC’s and WBC’s and dendritic cells Lymphoid B and T cells and dendritic cells

Fig 2 -1 Kuby, 5 e

Hematopoietic influences • Stromal cells influence diff of HSC by providing hematopoieticinducing microenvironment (HIM) with: -colony stimulating factor (CSF) -erythropoietin (EPO) • Cytokine influences -> stimulated by activated MØ and T cells • Genetic regulation – see Table 2 -1. • Hematopoietic homeostasis – req’d to maintain certain [c] of cells balance between cells removed by cell death and those produced -for WBC’s: a human must produce ~3. 7 x 1011/day ! *Each WBC has a specific life span + dies by apoptosis; Neutrophils live only a few days

Apoptosis – programmed cell death Process thru which cells die + later phago’d • decrease in cytoplasmic volume; apoptotic bodies • Clumping/break up of DNA • Phago’d by MØ blocks release of cyto contents no local inflam response It is influenced by gene expression • Chief among the genes is bcl 2 - inhibits cell death (Activ. lympho’s express lower levels of bcl 2 and are more susceptible to apoptosis) -If activ continues, the apoptic signal is blocked -If activ does not, lympho’s begin to die by apoptosis

Fig 2 -5

Hematopoietic stem cells can be enriched