Increased biodiversity in the environment improves the humoral response of rats

Abstract

Previous studies have compared the immune systems of wild and of laboratory rodents in an effort to determine how laboratory rodents differ from their naturally occurring relatives. This comparison serves as an indicator of what sorts of changes might exist between modern humans living in Western culture compared to our hunter-gatherer ancestors. However, immunological experiments on wild-caught animals are difficult and potentially confounded by increased levels of stress in the captive animals. In this study, the humoral immune responses of laboratory rats in a traditional laboratory environment and in an environment with enriched biodiversity were examined following immunization with a panel of antigens. Biodiversity enrichment included colonization of the laboratory animals with helminths and co-housing the laboratory animals with wild-caught rats. Increased biodiversity did not apparently affect the IgE response to peanut antigens following immunization with those antigens. However, animals housed in the enriched biodiversity setting demonstrated an increased mean humoral response to T-independent and T-dependent antigens and increased levels of "natural" antibodies directed at a xenogeneic protein and at an autologous tissue extract that were not used as immunogens.

Fig 1. Body weights of biome depleted and biome enriched rats at (A) 4 days old, (B) 23 days old, and (C) 63 days old.

The mean ± the standard error is indicated by the horizontal lines. No statistical significance (NS) was observed with comparing data from biome depleted and biome enriched animals using a t-test.

Fig 2. Relative concentration of IgE and of peanut-specific IgE in the serum of biome depleted (n = 20) and biome enriched (n = 15) rats following immunization.

The relative concentration of antibody was determined by ELISA as described in the Methods. The means and standard errors are indicated by the horizontal bars, and the data were assessed using a t-test. (A) Following immunization, no statistically significant difference (NS) was observed when comparing total serum IgE levels from biome depleted and biome enriched animals. In addition, (B), following immunization, no statistically significant difference (NS) was observed when comparing anti-peanut IgE levels from biome depleted and biome enriched animals.

Fig 3. Relative concentration of FITC-specific IgG in the serum of biome depleted (n = 20) and biome enriched (n = 15) rats.

The relative concentration of antibody was determined by ELISA as described in the Methods. The means and standard errors are shown. No statistical significance (NS) was observed with comparing data from biome depleted and biome enriched animals using a t-test.

Fig 4. Relative concentration of DNP-specific antibody in the serum of biome depleted (n = 20) and biome enriched (n = 15) rats.

The relative concentration of antibody was determined by ELISA as described in the Methods. Relative levels of (A) IgM, (B) IgG, and (C) subclasses of IgG are shown. The means and standard errors are shown. The p-values associated with comparing data from biome depleted and biome enriched animals using a t-test are shown. (NS = not significant)

Fig 5. Natural anti-human serum albumin antibody levels in the serum of biome depleted (n = 20) and biome enriched (n = 15) rats.

The relative concentration of antibody was determined by ELISA as described in the Methods. Relative levels of (A) IgM and (B) IgG are shown. Binding to human serum albumin (HSA) was used as a measure of reactivity toward a xenogeneic antigen for which the animals lacked previous exposure. The means, standard errors, and the p-values associated with comparing data from biome depleted and biome enriched animals using a t-test are shown. (NS = not significant)

Fig 6. Binding of natural anti-rat muscle IgM in the serum of biome depleted and biome enriched rats as evaluated by immunoblotting.

(A) Rat muscle extracts were separated by SDS PAGE and probed by immunoblotting as described in the Methods. The analysis was limited to 15 animals (n = 8 biome enriched; lanes E1 through E8, and n = 7 biome depleted; lanes D1 through D7) due to size constraints of the gel. A control strip with no serum is labeled “C”, and indicates reactivity of the anti-IgM conjugate with muscle-derived antigens. (B) The number of bands recognized by natural IgM in individual sera (p = 0.0089) and the total reactivity of natural IgM from each serum sample (p = 0.0093) are shown, with the bars indicating the mean and standard error. (C) The distribution of bands as a function of band size is shown. For this analysis, the average number of bands in biome depleted and biome enriched rats (Y-axis) was plotted on linear and log scales (main figure and figure inset, respectively) versus different band sizes (X-axis).

Fig 7. Binding of natural anti-rat muscle IgG in the serum of biome depleted and biome enriched rats as evaluated by immunoblotting.

(A) Rat muscle extracts were separated by SDS PAGE and probed by immunoblotting as described in the Methods. The analysis was limited to 15 animals (n = 8 biome enriched; lanes E1 through E8, and n = 7 biome depleted; lanes D1 through D7) due to size constraints of the gel. A control strip with no serum is labeled “C”, and indicates reactivity of the anti-IgG conjugate with muscle-derived antigens. (B) The number of bands recognized by natural IgG in individual sera (p = 0.017) and the total reactivity of natural IgG from each serum sample (p = 0.040) are shown, with the bars indicating the mean and standard error. (C) The distribution of bands as a function of band size is shown. For this analysis, the average number of bands in biome depleted and biome enriched rats (Y-axis) was plotted on linear and log scales (main figure and figure inset, respectively) versus different band sizes (X-axis).