Module 10 Short Summary

Despite several decades of research, findings on the effects of age on hemopoiesis and blood cell function remain equivocal. It appears that changes in other physiological systems (e.g., cardiorespiratory, renal function) have more of an effect than do intrinsic changes in the hemopoietic system, itself.

Although the numbers of blood cells may not be directly affected by age, there are some changes in function of lymphocytes and neutrophils in response to stress and challenge in elderly individuals. This is reflected in a decreased response to infections and other challenges in older individuals, which may lead to serious or lethal consequences.

1. Neutrophils from the elderly show a decrease in the total amount of lysozyme produced in response to an experimental challenge compared to neutrophils from younger individuals. This may indicate a decrease in the ability to fight infections.
   
   
   
2. There is also reduced T cell function in the elderly attributable to several findings:
   
   
   1. decreased synthesis of IL-2 receptors;
   2. decreased IL-2 production, itself;
   3. decreased ability of the CD3/T cell receptor complex to bind ligand, which results in cell activation;
   4. defects in the activation of protein kinase C-dependent transcription factors.
      
      
      
3. B cells defects include:
   
   
   1. reduced antibody response to both T-dependent and T-independent antigens;
   2. a decrease in isoagglutinins;
   3. an increase of autoantibodies and monoclonal gammopathies.
      
      

   The overall effect here is to lower the body’s ability to produce antibodies that are effective against a specific challenge from microorganisms in the environment.
   
   

4. Thymic involution. A decrease or loss of thymic hormone has been proposed to adversely affect the immune response, but there is conflicting data to support this hypothesis.