Which of the following is a common cause of lymphocytosis?

Lymphocytosis refers to an elevated level of lymphocytes, which are a type of white blood cell that plays a crucial role in the immune system, particularly in fighting off infections. Viral infections are well-known for causing lymphocytosis as they typically stimulate the immune response, leading to an increase in the production and activation of lymphocytes to combat the viral pathogens.

When the body encounters a viral infection, it produces specific lymphocytes—such as T cells and B cells—that target the virus. This increase in lymphocytes is a natural and expected response, reflecting the body's efforts to mount a defense against the infection. Common viral infections associated with lymphocytosis include influenza, hepatitis, and some forms of viral gastroenteritis.

In contrast, bacterial infections generally result in leukocytosis characterized by an increase in neutrophils, another type of white blood cell more specifically involved in fighting bacteria. Allergic reactions can lead to changes in other white blood cell types, such as eosinophils, rather than a primary increase in lymphocytes. Iron deficiency is not typically linked to lymphocytosis; instead, it may lead to conditions like anemia which does not primarily involve an increase in lymphocyte counts.

Therefore, the connection between viral infections and lymphocyt