Hormones Affecting Blood Cell Production &
Function
Hormones
• Erythropoietin
• Leukopoietin
• Thymosin
Erythropoietin
• 165 amino acid glycoprotein, MW = 30,000
• Produced primarily by peritubular capillary endothelial cells (Kidney)
• Minor production by Liver
• Receptor with a single transmembrane domain– Requires dimerization like PRL/GH receptor– Binds to and activates JAK-2
Erythropoietin Action
• In concert with other growth factors– Stimulates growth and maturation of
erythroblast line– Stimulates growth of megakaryocyte– Stimulates the initiation of
megakaryocyte process formation
Erythropoietin Control
PERITUBULARCAPILLARY
ENDOTHELIUM
pO2 pO2
ERYTHROBLASTLINE
ERYTHROPOIETIN
RBCs
Leukopoietin
• Postulated to Exist
• Stimulate production of Myeloid cells.
Thymic Hormones
• Thymic ablation in adult animals had no observable effect.
• Neonatal Thymectomy– Wasting Disease– Death from opportunistic infections
• Wasting Disease also after radiation & thymectomy.
• Wasting Disease prevented by thymic extracts--Thymosin
Thymosins
• Thymosin Fraction 5:– Crude preparation of 40-60 peptides– Enhances natural killer cell (NK-cell)
activity.– Stimulates secretion of Interleukin-2
(IL2) production– Stimulates IL2 receptor expression– Stimulates IL1 and tumor necrosis
factor (TNF) production
Thymosins (Cont.)
• Thymosin-alpha-1– 28 amino acid peptide– 113 amino acid prohormone,
prothymosin alpha– Induces differentiation of T-cell
precursors– Stimulates production of IL2, IL2
receptor & B-cell growth factor– Helper (CD4+) and cytotoxic (CD8+) T-
cells are target
Thymosins (Cont.)
• Thymosin-alpha-1 (Cont.)– Increases efficiency of antigen presentation
by antigen presenting cells– Paracrine/autocrine factor– Regulation not known
Thymosins (Cont.)
• Beta-thymosins– Group of related proteins who’s effect
on lymphocytes is poorly understood– May be induced by interferon– Thymosin-Beta-4 acts on differentiation
and maturation of early T-cells– Many of the beta-thymosins are
expressed by tumor cells and may be involved in metastasis.
Other Thymic Peptides
• Thymostimulin (TP-1)– Enhanced production of IL2 and interferon– Reduces postoperative infection rates of
immunocompromised patients
• Thymopoietin– Stimulates differentiation of T-cells while
inhibiting differentiation of B-cells– Increased IL2 and IL2 receptor expression– Increased size of T-cell pool– Increased NK-cell activity.
Other Thymic Peptides
• Thymulin (Serum thymic factor)– Increases T-cell populations probably
via stimulation of IL1– Production stimulated by PRL & GH
AIDS
• Thymic peptides have been used to enhance the immune system of HIV infected individuals.