Intermittent fasting favored the resolution of Salmonella typhimurium infection in middle-aged BALB/c mice

Abstract

Intermittent fasting (IF) reportedly increases resistance and intestinal IgA response to Salmonella typhimurium infection in mature mice. The aim of this study was to explore the effect of aging on the aforementioned improved immune response found with IF. Middle-aged male BALB/c mice were submitted to IF or ad libitum (AL) feeding for 40 weeks and then orally infected with S. typhimurium. Thereafter, infected animals were all fed AL (to maximize their viability) until sacrifice on day 7 or 14 post-infection. We evaluated body weight, bacterial load (in feces, Peyer's patches, spleen and liver), total and specific intestinal IgA, lamina propria IgA+ plasma cells, plasma corticosterone, and messenger RNA (mRNA) expression of α-chain, J-chain, and the polymeric immunoglobulin receptor (pIgR) in liver and intestinal mucosa. In comparison with the infected AL counterpart, the infected IF group (long-term IF followed by post-infection AL feeding) generally had lower intestinal and systemic bacterial loads as well as higher total IgA on both post-infection days. Both infected groups showed no differences in corticosterone levels, body weight, or food and caloric intake. The increase in intestinal IgA was associated with enhanced pIgR mRNA expression in the intestine (day 7) and liver. Thus, to maintain body weight and caloric intake, IF elicited metabolic signals that possibly induced the increased hepatic and intestinal pIgR mRNA expression found. The increase in IgA probably resulted from intestinal IgA transcytosis via pIgR. This IgA response along with phagocyte-induced killing of bacteria in systemic organs (not measured) may explain the resolution of the S. typhimurium infection.

Keywords: Intermittent fasting; Intestinal IgA; Liver polymeric immunoglobulin receptor; Middle-aged mice; Salmonella typhimurium infection.

Fig. 1

Experimental protocol. After being individually housed and fed ad libitum from the 8 to 18 weeks of life, two groups of BALB/c mice were formed, each subjected to a distinct dietary protocol from 19 to 59 weeks of life: (a) intermittent fasting and (b) ad libitum feeding. At 60 weeks of life, each of these two groups was divided into an uninfected and two infected subgroups. The uninfected subgroup (n = 7) from each dietary regimen was sacrificed at 61 weeks of life. The other mice from each dietary regimen (n = 14) were sublethally infected at 60 weeks of life by intragastric route with S. typhimurium. Afterward, all infected animals were fed ad libitum in order to maximize their viability. Half of the infected mice from each dietary regimen (n = 7) were sacrificed on day 7 and the other half (n = 7) on day 14 post-infection, corresponding to the 61st and 62nd week of life, respectively

Fig. 2

Bacterial load in samples from the groups with intermittent fasting and ad libitum feeding that were infected with S. typhimurium. Colony-forming units per gram of sample (CFU × 10⁶/g) are expressed as the mean ± standard deviation (SD) from one representative assay of three independent assays carried out. a CFU × 10⁶/g recorded daily in feces during 14 days post-infection expressed as the mean ± SD of 12 mice per group for days 1–7 and 6 mice per group for days 8–14. CFU per gram was expressed as the mean ± SD of six mice per group was recorded on days 7 and 14 post-infection in the following: b Peyer’s patches, c spleen, and d liver. Significant differences were found: (i) between the infected and uninfected (basal = Ctrl) groups within each dietary regimen (***p < 0.001), (ii) between infected mice with long-term intermittent fasting (followed by ad libitum feeding) and infected animals with long-term ad libitum feeding, at day 7 and day14 post-infection, and (iii) between the two infected subgroups of each dietary regimen, comparing day 7 with day 14 post-infection (p value above solid line)

Fig. 3

From intestinal supernatants in mice with long-term intermittent fasting (followed by 2 weeks of ad libitum feeding post-infection) and from animals with long-term ad libitum feeding, levels were determined of a total IgA in microgram per milliliter and b specific IgA to Salmonella typhimurium in absorbance values at λ = 490 nm (A _490 nm). From intestinal lamina propia, determination was made of c the frequency of IgA+ plasma cells (expressed as percentage of IgA+ relative to the total CD19+ CD138+ plasma cells). Values are expressed as the mean ± SD of six mice per group from one representative assay. Significant differences existed (i) between the infected vs uninfected (Ctrl) subgroups within each dietary regimen (***p < 0.001 or p = 0.005 for total IgA of infected ad libitum group day 7), (ii) between infected mice with intermittent fasting and infected animals with ad libitum feeding, at day 7 and day 14 post-infection, and (iii) between the two infected subgroups of each dietary regimen, comparing day 7 with day 14 post-infection (p value above solid line)

Fig. 4

In mice with long-term intermittent fasting (followed by 2 weeks of ad libitum feeding post-infection) and animals with long-term ad libitum feeding, determinations were made of intestinal mRNA expression of a α-chain, b J-chain, and c pIgR. Values are expressed as the mean ± SD of six mice per group. Significant differences existed (i) between the infected and uninfected (Ctrl) groups within each dietary regimen (***p < 0.001 or p = 0.018 for α-chain mRNA of infected ad libitum group day 7), (ii) between infected mice with intermittent fasting and infected animals with ad libitum feeding, at day 7 and day 14 post-infection, and (iii) between the two infected subgroups of each dietary regimen, comparing day 7 with day 14 post-infection (p value above solid line)

Fig. 5

In mice with long-term intermittent fasting (followed by 2 weeks of ad libitum feeding post-infection) and animals with long-term ad libitum feeding, determinations were made of hepatic mRNA expression of a α-chain, b J-chain, and c pIgR. Values are expressed as the mean ± SD of six mice per group. Significant differences existed (i) between the infected and uninfected (Ctrl) groups within each dietary regimen (***p < 0.001 or p = 0.042 for α-chain mRNA of the infected ad libitum group at day 7), (ii) between infected mice with intermittent fasting and infected animals with ad libitum feeding, at day 7 and day 14 post-infection, and (iii) between the two infected subgroups of each dietary regimen, comparing day 7 with day 14 post-infection (p value above solid line)

Fig. 6

In mice with long-term intermittent fasting (followed by 2 weeks of ad libitum feeding post-infection) and animals with long-term ad libitum feeding, determinations were made of plasma corticosterone levels (ng/mL). Values are expressed as the mean ± SD of six mice per group. Significant differences existed (i) between the infected and uninfected (Ctrl) groups within each dietary regimen (***p < 0.001), (ii) between infected mice with intermittent fasting and infected animals with ad libitum feeding, at day 7 and day 14 post-infection, and (iii) between the two infected subgroups of each dietary regimen, comparing day 7 with day 14 post-infection (p value above solid line)