Involvement of CD4 + and CD8 + T-lymphocytes in the modulation of nociceptive processing evoked by CCL4 in mice.

Aims: To explore the mechanisms involved in the transformation of analgesia produced by low doses of CCL4 (pg/kg) to hyperalgesia when higher doses (ng/kg) are administered to mice.
Main Methods: The unilateral hot plate test was used to assess thermal nociception. CD3 ⁺ , CD4 ⁺ or CD8 ⁺ blood cells were depleted with selective antibodies. Expression of CCR5 and IL-16 in lymphocytes was studied by flow cytometry and IL-16 blood levels were measured by ELISA. IL-16 and CD8 were detected by immunofluorescence.
Key Findings: IL-16 and CCR5 expression were demonstrated in CD4 ⁺ and CD8 ⁺ T-lymphocytes by flow cytometry. Furthermore, CCL4-induced hyperalgesia was abolished by reducing circulating T-lymphocyte levels or by selectively depleting CD4 ⁺ lymphocytes. In contrast, when the anti-CD4 antibody was acutely administered, CCL4 induced analgesia instead of hyperalgesia. A similar response was obtained when administering A-770041, that prevents CD4-mediated CCR5 desensitization by inhibiting p56 ^lck kinase. As occurred with the analgesic effect evoked by low doses of CCL4, analgesia evoked by combining CCL4 and A-770041 was reverted by naloxone, naltrindole or an anti-met-enk antibody. Interestingly, flow cytometry assays showed that the number of CD8 ⁺ , but not CD4 ⁺ , T-cells expressing IL-16 is reduced after the acute administration of CCL4, a result compatible with the description that CD8 ⁺ -lymphocytes can rapidly release preformed IL-16. Accordingly, the rise in IL-16 blood concentration evoked by CCL4 was prevented after CD8 ⁺ lymphocyte depletion.
Significance: CCL4-evoked hyperalgesia is related to the desensitization of CCR5 in CD4 ⁺ T-cells and to the release of IL-16 from CD8 ⁺ lymphocytes.
(Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)