The correct answer is:
c. Afferent lymphatics
Naïve lymphocytes enter the lymph nodes through afferent lymphatic vessels. These vessels carry the lymph, which contains lymphocytes, from peripheral tissues towards the lymph nodes. The afferent lymphatics bring the naïve lymphocytes into the subcapsular sinus of the lymph node, where they can encounter antigens and initiate immune responses. Efferent lymphatics, on the other hand, carry the filtered and antigen-presenting cells-enriched lymph out of the lymph nodes. Veins and arteries are not directly involved in naïve lymphocyte entry into the lymph nodes. High endothelial venules (HEVs) are specialized postcapillary venules found in the paracortex region of secondary lymphoid organs, including lymph nodes, where they facilitate extravasation of circulating naïve lymphocytes into the organ.
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