Probiotics exert several health beneficial effects to the host by several potential systems through the local immunity and systemic immunity (by enhancing specific and non-specific immune system). The application of probiotics is efficient and competent for several ailments, including virus infection.

Probiotics modulate the host’s innate immune system by enhancing phagocytic activity, leucocytes (polymorphonuclear and monocytes), and expression of some receptors (CR1, CR3, FccRI and FcaR) that are associated with phagocytosis, and increases the microbicidal function of neutrophils. The number and the activity of natural killer (NK) cells are also significantly improved in the blood.

Probiotics also can induce APCs derived pro- and anti inflammatory cytokine (for example, IL-10, IL-12, IL-17, TNF-α, interferon-α) production against foreign particles through activation of adaptive immunity. Intestinal inflammation regulatory pro-inflammatory cytokines, chemokines and their receptors are inhibited by anti-inflammatory cytokine IL10, produced by different immune-activated cells.  Probiotics provide two different immune-modulatory effects: one is the immune-stimulatory effect, which activates IL-12 production, induces NK, Th1, and Th2 cells, and acts against infection and allergy; and another type is immune-regulatory effect, which induces IL-10 and Treg cell activation by Th2, DCs & B cells.

Oral consumption of lactobacilli can modulate cytokine profiles systemically. Lactobacillus GG and Lb casei strains, Shirota (LcS) and DN114001, can prevent and treat the microbial infections in the gastrointestinal and respiratory tract with influenza. Consumption of Bifidobacterium breve–augmented antiinfluenza IgG could successfully protect respiratory tract infections in mice against influenza. Compared with the healthy adults and the elderly, the immune compromised elderly population contain reduced diversity and a lower number of the intestinal microbial community ofFirmicutes, Bifidobacteria, Clostridium, Faecalibacterium, Prausnitzii, and Blautia coccoides-Eubacterium rectal and higher occurrence of Enterobacteriaceae and Bacteroidetes.

Aging affects both innate and adaptive immune responses. Appropriate probiotics significantly can boost immunity in the elderly. The efficiency of treatment of older adults with Bif. lactis DN173010 and Lb. casei Shirota is responsible for the production of short-chain fatty acids like butyric acid, propionic acid, lactic acid and decreased the colonic pH value that increased the peristalsis in the colon which is capable of decreasing the intestinal transit time.. Administration of a fermented dairy product containing the probiotic strain Lb. casei DN-114 001 could decrease the duration of common infectious diseases (CID) of the airways, especially in rhinopharyngitis in the elderly in comparison with the control group.

Probiotics are also responsible for reducing the risk of chances of ventilator associated pneumonia; other respiratory infection in healthy and diseased person and 40–60% virus infected chronic obstructive pulmonary diseases (COPD) are prevented by administration of probiotic . Probiotic consumption decreases the risk of respiratory tract infection in children. The utilization of probiotics fundamentally diminishes the danger of the basic cold and lessens the duration of the manifestations of respiratory tract infections. In addition, probiotics showed a significant role in competitively colonizing in the gut to exclude pathogens, modulating the gut barrier functions and permeability. It has been shown earlier that probiotics can increase the neutrophil, leukocyte, and natural killer cell counts and activity.