Which body fluid typically contains no erythrocytes and less than 25 nucleated cells per microliter?

Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissues that surround the brain and spinal cord. Typically, healthy CSF contains very few cells, usually less than 5 nucleated cells per microliter, with most of these being lymphocytes. The presence of erythrocytes is generally absent in normal CSF, as any significant number of red blood cells can indicate bleeding or a pathological condition. Therefore, the defining characteristics of cerebrospinal fluid fit the criteria of having no erythrocytes and fewer than 25 nucleated cells per microliter, making it the correct choice.

In contrast, synovial fluid, while it can contain fewer than 25 nucleated cells per microliter in healthy conditions, may also have higher counts in inflammatory or arthritic conditions, thus not consistently meeting the criteria. Aqueous humor, located in the eye, can have different cellular compositions and is not typically analyzed in the same contexts as CSF. Plasma, a component of blood, contains a significant number of both erythrocytes and nucleated cells, and is not relevant to this question's criteria.