Final answer:
The primary cause of an impaired humoral response in older adults is immunosenescence, which includes the shrinking of the thymus gland and a subsequent decrease in the production of naïve T cells, adversely affecting antibody production and the overall humoral response.
Step-by-step explanation:
The primary cause of an impaired humoral response in older adults is due to immunosenescence, a process associated with the aging of the immune system. As individuals age, the thymus gland undergoes thymic involution, which means it gradually shrinks and reduces its function. This decline in thymic function leads to a decreased production of naïve T cells, which are essential for the prompt and efficient response to new antigens. Consequently, this affects the body's ability to mount an effective humoral immune response, which is the aspect of immunity that is responsible for the production of antibodies.
Furthermore, older adults often experience a decline in B cell function, leading to lower antibody diversity and production. The elderly are thus more susceptible to infections, more prone to develop chronic diseases, and often have a reduced response to vaccinations. This decrease in humoral immunity is compounded by other factors like metabolic disturbances, poor diet, and stress, which can contribute to secondary immunodeficiency in addition to the primary agerelated changes.