Training of Primary Chicken Monocytes Results in Enhanced Pro-Inflammatory Responses

Abstract

Beta-glucan-stimulated mammalian myeloid cells, such as macrophages, show an increased responsiveness to secondary stimulation in a nonspecific manner. This phenomenon is known as trained innate immunity and is important to prevent reinfections. Trained innate immunity seems to be an evolutionary conserved phenomenon among plants, invertebrates and mammalian species. Our study aimed to explore the training of primary chicken monocytes. We hypothesized that primary chicken monocytes, similar to their mammalian counterparts, can be trained with β-glucan resulting in increased responses of these cells to a secondary stimulus. Primary blood monocytes of white leghorn chickens were primary stimulated with β-glucan microparticulates (M-βG), lipopolysaccharide (LPS), recombinant chicken interleukin-4 (IL-4) or combinations of these components for 48 h. On day 6, the primary stimulated cells were secondary stimulated with LPS. Nitric oxide (NO) production levels were measured as an indicator of pro-inflammatory activity. In addition, the cells were analyzed by flow cytometry to characterize the population of trained cells and to investigate the expression of surface markers associated with activation. After the secondary LPS stimulation, surface expression of colony stimulating factor 1 receptor (CSF1R) and the activation markers CD40 and major histocompatibility complex class II (MHC-II) was higher on macrophages that were trained with a combination of M-βG and IL-4 compared to unstimulated cells. This increased expression was paralleled by enhanced NO production. In conclusion, this study showed that trained innate immunity can be induced in primary chicken monocytes with β-glucan, which is in line with previous experiments in mammalian species. Innate immune training may have the potential to improve health and vaccination strategies within the poultry sector.

Extracellular trap can be trained as a memory response

“…Re-challenge with C. perfringens (MOI = 5) resulted in a significantly higher release of extracellular DNA in HK- C. albicans -primed PBMC ( Figure 4(b) ), thereby it showed increased the ability to kill bacteria of PBMC ( Figure 4(c) ). Consistent with previous reports about trained immunity in chicken [ 28 ], we observed an increased production of antimicrobial NO upon stimulation with C. perfringens (MOI = 10) is stronger in HK- C. albicans -primed PBMCs compared to non-primed PBMCs ( Figure 4(d) ). Unstimulated cells were used as controls for the basal level.…”

“…Trained immunity is an evolutionarily conservative innate immune mechanism that exists in multiple vertebrate species including mammals [ 26 ], chickens [ 28 ], and fishes [ 42 ]. This study showed that exposure to C. perfringens increases the production of NO in primed PBMC compared to non-primed.…”

Trained Immunity as an Adaptive Branch of Innate Immunity

“…In dogs, β-glucan improved the action of an inactivated rabies vaccine by stimulation of both B and T lymphocytes [ 103 ]. β-Glucan was also found to induce significant trained immunity in chicken monocytes, similarly to mammals [ 104 ]. So far, no epigenetic changes have been found, but this is probably due to the limited number of studies using avian models.…”

Effects of Newcastle Disease/Infectious Bronchitis Vaccine and Feeding Yeast Products on the Innate Immune System in the Proventriculus and Ileum of Broiler Chicks

“…β-Glucan was reported to increase phagocytosis, bactericidal activity, and oxidative burst in chicks ( Lowry et al, 2005 ). β-Glucan treatment could also induce trained innate immunity in primary chicken monocytes ( Verwoolde et al, 2020 ). A study in humans also suggested that β-glucan induces trained immunity by enriching histone modification at the promoter regions of proinflammatory genes in human monocytes ( Domínguez-Andrés et al, 2020 ).…”