Pyeung-Hyeun Kim

Jang YS, et al. Immune Netw. 2023 Sep;23(5):e37. https://doi.org/10.4110/in.2023.23.e37

We recently reported that lactoferrin (LF) induces Foxp3(+) Treg differentiation through binding to TGF beta receptor III (T beta RIII), and this activity was further enhanced by TGF beta 1. Generally, a low T-cell receptor (TCR) signal strength is favourable for Foxp3(+) Treg differentiation. In the present study, we explored the effect of lactoferrin chimera (LFch, containing lactoferricin [aa 17-30] and lactoferrampin [aa 265-2841), along with TGF beta 1 on Foxp3(+) Treg differentiation. LFch alone did not induce Foxp3 expression, yet LFch dramatically enhanced TGF beta 1-induced Foxp3 expression. LFch had little effect on the phosphorylation of Smad3, a canonical transcriptional factor of TGF beta 1. Instead, LFch attenuated the phosphorylation of S6 (a target of mTOR), I kappa B and PI3K. These activities of LFch were completely abrogated by pretreatment of LFch with soluble TGF beta 1 receptor III (sT beta RIII). Consistent with this, the activity of LFch on TGF beta 1-induced Foxp3 expression was also abrogated by treatment with sT beta RIII. Finally, the TGF beta 1/LFchinduced T cell population substantially suppressed the proliferation of responder CD4(+) T cells. These results indicate that LFch robustly enhances TGF beta 1-induced Foxp3(+) Treg differentiation by diminishing TCR/CD28 signal intensity.

Lactoferrin (LF) is known to possess anti-inflammatory activity, although its mechanisms of action are not well-understood. The present study asked whether LF affects the commitment of inducible regulatory T cells (Tregs). LF substantially promoted Foxp3 expression by mouse activated CD4⁺T cells, and this activity was further enhanced by TGF-β1. Interestingly, blocking TGF-β with anti–TGF-β Ab completely abolished LF-induced Foxp3 expression. However, no significant amount of soluble TGF-β was released by LF-stimulated T cells, suggesting that membrane TGF-β (mTGF-β) is associated. Subsequently, it was found that LF binds to TGF-β receptor III, which induces reactive oxygen species production and diminishes the expression of mTGF-β–bound latency-associated peptide, leading to the activation of mTGF-β. It was followed by phosphorylation of Smad3 and enhanced Foxp3 expression. These results suggest that LF induces Foxp3⁺ Tregs through TGF-β receptor III/reactive oxygen species–mediated mTGF-β activation, triggering canonical Smad3-dependent signaling. Finally, we found that the suppressive activity of LF-induced Tregs is facilitated mainly by CD39/CD73-induced adenosine generation and that this suppressor activity alleviates inflammatory bowel disease. Key Points Lactoferrin induces Foxp3⁺ Tregs via TβRIII→ROS→mTGF-β activation→Smad3 signaling. Suppression by these Tregs exerts through CD39/CD73-mediated adenosine generation. Peroral administration of lactoferrin alleviates DSS-induced colitis. Visual Abstract

The effector function of tumor-infiltrated CD4⁺ T cells is readily suppressed by many types of immune regulators in the tumor microenvironment, which is one of the major mechanisms of immune tolerance against cancer. Cathelicidin-related antimicrobial peptide (CRAMP), the mouse analog of LL-37 peptide in humans, is a cationic antimicrobial peptide belonging to the cathelicidin family; however, its secretion by cancer cells and role in the tumor microenvironment (TME) remain unclear. In this study, we explored the possibility of an interaction between effector CD4⁺ T cells and CRAMP using in vitro-generated mouse Th17 cells. We found that CRAMP stimulates Th17 cells to express the ectonucleotidase CD73, while simultaneously inducing cell death. This finding suggested that CD73-expressing Th17 cells may function as immune suppressor cells instead of effector cells. In addition, treatment of pharmacological inhibitors of the transforming growth factor-beta (TGF-β) signaling pathway showed that induction of CD73 expression is mediated by the p38 signaling pathway. Overall, our findings suggest that tumor-derived LL-37 likely functions as an immune suppressor that induces immune tolerance against tumors through shaping effector Th17 cells into suppressor Th17 cells, suggesting a new intervention target to improve cancer immunotherapy.

Park HW, et al. Immune Netw. 2020 Oct;20(5):e38. https://doi.org/10.4110/in.2020.20.e38

γδ T cells are abundant in the gut mucosa and play an important role in adaptive immunity as well as innate immunity. Although γδ T cells are supposed to be associated with the enhancement of Ab production, the status of γδ T cells, particularly in the synthesis of IgA isotype, remains unclear. We compared Ig expression in T cell receptor delta chain deficient (TCRδ-/-) mice with wild-type mice. The amount of IgA in fecal pellets was substantially elevated in TCRδ-/- mice. This was paralleled by an increase in surface IgA expression and total IgA production by Peyer's patches (PPs) and mesenteric lymph node (MLN) cells. Likewise, the TCRδ-/- mice produced much higher levels of serum IgA isotype. Here, surface IgA expression and number of IgA secreting cells were also elevated in the culture of spleen and bone marrow (BM) B cells. Germ-line α transcript, an indicator of IgA class switch recombination, higher in PP and MLN B cells from TCRδ-/- mice, while it was not seen in inactivated B cells. Nevertheless, the frequency of IgA+ B cells was much higher in the spleen from TCRδ-/- mice. These results suggest that γδ T cells control the early phase of B cells, in order to prevent unnecessary IgA isotype switching. Furthermore, this regulatory role of γδ T cells had lasting effects on the long-lived IgA-producing plasma cells in the BM.

Lactoferrin (LF) and retinoic acid (RA) are enriched in colostrum, milk, and mucosal tissues. We recently showed that LF-induced IgA class switching through binding to betaglycan (transforming growth factor-beta receptor III, TβRIII) and activation of canonical TGF-β signaling. We investigated the combined effect of LF and RA on the overall IgA response. An increase in IgA production by LF was further augmented by RA. This combination effect was also evident in Ig germ-line α (GLα) transcription and GLα promoter activity, indicating that LF in cooperation with RA increased IgA isotype switching. We subsequently found that RA enhanced TβRIII expression and that this increase contributed to LF-stimulated IgA production. In addition to the IgA response, LF and RA in combination also enhanced the expression of the gut-homing molecules C-C chemokine receptor 9 (CCR9) and α4β7 on B cells. Finally, peroral administration of LF and RA enhanced the frequency of CCR9⁺IgA⁺ plasma cells in the lamina propria. Taken together, these results suggest that LF in cooperation with RA can contribute to the establishment of gut IgA responses.

Kang SH, et al. Immune Netw. 2015 Feb;15(1):37-43. https://doi.org/10.4110/in.2015.15.1.37