Increase Immunity/Bacterial Resistance

Lactic acid bacteria have been shown to enhance immune response, increasing resistance to infection.^{4,6,11,16-20,34} Wakunaga's Bifidobacteria and L. acidophilus have been shown to activate macrophages which produce substances that suppress harmful bacteria.^4,6,11 In addition, L. acidophilus has been shown to improve macrophage phagocytic capacity, or the ability of these immune cells to engulf and remove foreign organisms. Further, supplementation of lactobacillus  in diets has been shown to enhance the clearance or removal of the intraveniously injected gram-negative bacterium, E.coli.¹⁶ 

L. acidophilus intake also doubled the amount of Kupffer (immune) cells, which are responsible for the clearance of circulating bacteria.¹⁶ Consumption of L. acidophilus and B. bifidum together caused a four-fold increase in IgA (Immunoglobulin A) against Salmonella typhi Ty21a when human subjects consumed bacteria prior to infection with this organism.¹⁷ 

Secretory IgA is an immunoglobulin which protects the mucosal lining of the intestinal tract by coating pathogens and hindering their attachment to the mucosa.^17,18 Even if live bacteria reach the intestines as dead bacteria, or as live bacteria which have died from exposure to gastric acid, bile or intestinal juice, the bacteria components, such as the cell walls of the lactic acid bacteria, are absorbed into the body, thus enhancing the defense mechanism.^16,19