Interleukin-6 (IL-6) and Type I Interferon (INF) signaling are necessary to induce neuronal death by Brucella abortus-activated microglia

JULIA RODRÍGUEZ; JULIA DE SANTIS ARÉVALO; ANA M. RODRÍGUEZ; GUILLERMO H. GIAMBARTOLOMEI

San Luis

Congreso; LXXI Reunión Anual de la Sociedad Argentina de Inmunología (SAI); 2023

Sociedad Argentina de Inmunología (SAI)

Neurobrucellosis is an inflammatory disease caused by Brucella spp infection of the central nervous system. We have previously demonstrated that B. abortus-infected microglia induces neuronal death through primary phagocytosis of live neurons. This particular mechanism of cellular death involves the activation of microglia and requires 2 conditions to take place: the secretion of nitric oxide and the increase in microglial phagocytic capacity. Since IL-6 and type I IFN have been implicated in the modulation of diverse neuropathological diseases; and considering that activated microglia are capable of secrete various pro-inflammatory mediators, we aimed to investigate the role of these cytokines on primary phagocytosis. Neurons/microglia co-cultures from BALB/c mice were infected or not with B. abortus for 48 h, in the presence of IL-6, IFN-β or IFNAR (type I interferon receptor) neutralizing antibodies or isotype control. After that, neuronal density in co-cultures was evaluated by fluorescence microscopy. Neutralization of IL-6 (p<0.005), IFN-β (p<0.05) and IFNAR (p<0.05) completely inhibited neuronal loss caused by B.abortus-infected microglia, indicating their relevance in this phenomenon. To evaluate in which of the two requirements each cytokine is involved, we measured nitric oxide secretion by the colorimetric Griess reaction and microglial phagocytic activity by a phagocytosis assay with negatively-charged fluorescent beads in presence of anti-IL-6, anti IFNAR or anti-IFN-β neutralizing antibodies. Neutralization of IL-6 significantly (p<0.05) decrease phagocytic activity (both the number of phagocytic microglia and the number of beads taken per microglia), but it did not affect secretion of nitric oxide (p>0.05) by activated-microglia. Conversely, neutralization of IFN-β did not modified phagocytosis activity (p>0.05) of B. abortus-activated microglia, but significantly decrease nitric oxide secretion (p<0.05). Altogether these results indicate that both IL-6 and IFN-β signaling pathways are necessary to induce phagocytosis of viable neurons by B. abortus-infected microglia. Moreover, our results demonstrate that these signaling pathways have independent effects on microglia functions and highlight their key role in this mechanism of neuronal death caused by B. abortus-infected microglia.