Intestinal IgA+ Cell Numbers as well as IgA, IgG, and IgM Contents Correlate with Mucosal Humoral Immunity of Broilers During Supplementation with High Fluorine in the Diets

Fluoride (F), a well-recognized harmful substance, is easily absorbed by the intestinal mucosa. The intestinal mucosal immune system is equipped with unique innate and adaptive defense mechanisms that provide a first line of protection against infectious agents. Meanwhile, immunoglobulins are the major secretory products of the adaptive immune system and their levels can be a strong indicator of a disease or condition. In this study, therefore, we investigated the effects of high dietary fluorine on the numbers of immunoglobulin A-positive (IgA⁺) cells in the lamina propria of intestines (duodenum, jejunum and ileum) by immunohistochemistry as well as on the contents of immunoglobulin A (IgA), immunoglobulin G (IgG), and immunoglobulin M (IgM) in the mucosa of intestines (duodenum, jejunum, and ileum) by enzyme-linked immunosorbent assay (ELISA). A total of 280 1-day-old healthy avian broilers were randomly divided into four groups and fed on a corn–soybean basal diet as control diet (fluorine 22.6 mg/kg) or the same basal diet supplemented with 400, 800, and 1,200 mg/kg fluorine (high fluorine groups I, II, and III) in the form of sodium fluoride (NaF) for 42 days. The experimental data showed that the numbers of IgA⁺ cells as well as the IgA, IgG, and IgM contents were significantly decreased (P < 0.01 or P < 0.05) in the high fluorine groups II and III when compared with those of the control group. It was concluded that dietary fluorine in the range of 800–1,200 mg/kg significantly reduced the numbers of the IgA⁺ cells and the contents of aforementioned immunoglobulins in the intestines (duodenum, jejunum, and ileum) of broilers, which could finally impact the mucosal humoral immune function in the intestines by a way that reduces the lymphocyte population and/or lymphocyte activation.