Where does a normal biodistribution of 111In labeled leukocytes show the greatest uptake 24 hours after injection?

The biodistribution of indium-111 labeled leukocytes, particularly 24 hours after injection, primarily highlights the splenic uptake. After the radiolabeled leukocytes are injected, they circulate in the bloodstream and migrate to areas of inflammation or infection within the body. However, the spleen serves as a critical organ for the storage and filtering of blood, and it plays a significant role in immune responses.

Leukocytes, including both neutrophils and lymphocytes, are known to localize in the spleen where they filter the blood and help mount immune responses to pathogens. This localization results in a notable accumulation of the radiolabeled leukocytes within the spleen, reflecting its essential function in hosting immune cells and responding to various immunological challenges.

While the liver, lungs, and bone marrow do play roles in the overall circulation and function of leukocytes, they do not exhibit the same level of selective uptake of these radiolabeled cells compared to the spleen, particularly at the 24-hour mark post-injection. Thus, recognizing that the spleen has a heightened role in this context elucidates why it is the site of greatest uptake in a normal biodistribution scenario for 111In labeled leukocytes.