Question

Which of the following is incorrect regarding sphingosine 1-phosphate (S1P) and its receptor?

1) It is a lipid that has chemotactic activity.
2) S1P gradients are established in lymph nodes with lowest concentrations in T-cell areas.
3) CD69 upregulates S1P receptor expression on the surface of naive T cells.
4) S1P is synthesized by all cells.

Answer 1

The incorrect statement regarding sphingosine 1-phosphate (S1P) and its receptor is that CD69 upregulates S1P receptor expression on the surface of naive T cells; in reality, CD69 downregulates this expression. S1P is a lipid with chemotactic activity, but it is not synthesized by all cells, and its gradients are not lowest in T-cell areas of lymph nodes.

Step-by-step explanation:

Sphingosine 1-Phosphate and Its Receptor

The question regarding the characteristics of sphingosine 1-phosphate (S1P) and its receptor involves identifying the incorrect statement from a given list. To address this question, it is crucial to understand the properties and functions of S1P, as well as its interaction with cellular receptors.

Firstly, S1P is indeed a lipid with chemotactic activity, which is the ability to direct cell movement towards or away from certain environments—this is point 1 and it is correct.

Regarding point 2, S1P gradients are established in lymphatic tissues. Typically, S1P concentrations are higher in the lymph and blood than in the tissue, facilitating the egress of T-cells from the lymph nodes, which opposes the statement in point 2 that the lowest concentrations are found in T-cell areas.

As for point 3, CD69 actually functions to downregulate the expression of the S1P receptor on T-cells, ensuring the retention of T-cells within lymph nodes during activation, rather than upregulating it as stated. Therefore, point 3 is incorrect.

Finally, point 4, which suggests that S1P is synthesized by all cells, is overly inclusive. Although S1P is widely produced, certain cells such as erythrocytes and endothelial cells are primarily responsible for the production of S1P found in the blood and lymph.

In conclusion, the statement that is incorrect with respect to S1P and its receptor is that CD69 upregulates S1P receptor expression on the surface of naive T cells. S1P plays a pivotal role in immune cell trafficking and lymphocyte circulation, and surface expression of its receptor is crucial for these processes.