The immune responses triggered by measles virus (MV) infection can unexpectedly suppress the body's ability to respond to other unrelated antigens, a condition that may persist for weeks to years after the acute illness subsides. This immune suppression significantly increases vulnerability to secondary bacterial and viral infections such as pneumonia and diarrhea, which are major causes of illness and death following measles.
Measles infection disrupts delayed-type hypersensitivity (DTH) responses to known antigens like tuberculin, and impairs both cellular and humoral responses to new antigens. This immune dysregulation also contributes to the reactivation of tuberculosis and the worsening of autoimmune diseases post-measles.
In essence, measles-induced immune suppression not only weakens immediate defenses against pathogens but also compromises the immune system's ability to mount effective responses to a range of antigens over an extended period.
Measles-induced immune suppression can occur due to changes in antigen-presenting cells or effector lymphocytes, or through the depletion of CD150+ memory lymphocytes. Measles virus (MV) infects CD150+ immune cells, including memory T- and B-lymphocytes. Studies comparing blood samples collected from unvaccinated children before and after measles reveal incomplete reformation of B-lymphocyte pools post-infection. Additionally, measles leads to a significant reduction in circulating antibodies against various viruses and bacteria, impairing immunological memory and causing what is termed 'immune amnesia'.
This mechanism contributes to increased childhood morbidity and mortality for more than two years after measles infection. Abnormalities in both innate and adaptive immune responses are evident following MV infection. Children commonly experience transient lymphopenia, characterized by decreased T and B lymphocytes in the blood. Furthermore, immune cells such as dendritic cells, crucial for presenting antigens to lymphocytes, show impaired maturation and reduced ability to stimulate lymphocyte proliferation.
In summary, measles disrupts immune function by compromising both cellular and antibody-mediated immunity, leading to prolonged susceptibility to infections and contributing to the severity of measles-related complications in children.
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