1. 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

2. 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

3. Fig 2-1 Kuby, 5e

4. Hematopoietic influences Stromal cells influence diff of HSC by providing hematopoietic- inducing 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 10 11 /day ! *Each WBC has a specific life span + dies by apoptosis; Neutrophils live only a few days

5. 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 bcl2 - inhibits cell death (Activ. lympho’s express lower levels of bcl2 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

6. Fig 2-5

7. Hematopoietic stem cells can be enriched