Research has shown that prophylactic treatment, specifically with the probiotic Lactobacillus species, is a viable natural alternative in the treatment and possible prevention of allergic diseases. Lactobacillus acidophilus strain L-92 (L-92), a bacterial strain used widely in dietary supplements, cultured milk, and yogurt in Japan, has been shown to have potent antiallergic activity both in vitro and in vivo. This review summarizes and explores previous published research on L-92, including its proposed mechanisms of action based on animal and laboratory studies and evidence from clinical trials supporting its use in treatment of allergic diseases.
The incidence of allergic diseases, such as allergic rhinitis and atopic dermatitis, has been on the rise in many industrial countries.1 The most widely accepted explanation for this phenomenon is known as the “hygiene hypothesis,” which postulates that a number of environmental factors occurring in Western societies are hindering proper development of the immune system. These factors, such as excessive hygiene and cleanliness, the increased use of antibiotics, and smaller family size, have resulted in reduced early childhood exposure to viruses and microorganisms, thus altering T helper (Th) homeostasis between type 1 helper cell (Th1) and type 2 helper cell (Th2), commonly expressed as Th1/Th2.2,3
The response to infectious stimuli normally elicits production of Th1 cells, the Th cells that drive cellular immunity, fighting pathogens and viruses inside the cell by producing inflammatory cytokines such as interleukin (IL)-2, interferon (IFN)-γ, and tumor necrosis factor (TNF)-α. On the other hand, Th2 cells drive humoral immunity, fighting foreign invaders and substances outside the cell by inducing the immunoglobulin (Ig)E‒mediated allergic reaction. Since the production of Th1 cells also downregulates production of Th2 cells and vice versa, it is theorized that immune regulation is achieved through a homeostasis between Th1 and Th2 activity. Imbalances of either type of Th cell can lead to disease. Th1 dominance may result in autoimmune disorders, and allergic conditions are linked to Th2 dominance.3-5
When exposure to infectious stimuli is reduced in early childhood, it is believed to lead to an overactive Th2 response.6,7 In one of the first (of many) revisions to the original hygiene hypothesis, Wold proposed that by limiting exposure to viruses or pathogenic bacteria, the overly hygienic lifestyle in industrialized countries alters the normal intestinal colonization pattern in infancy, leading to a failure to induce and maintain oral tolerance of innocuous allergens.8 This theory is also supported by studies that have shown associations between the composition of intestinal microbiota and allergic diseases.9,10
With no known interventions that “cure” allergic diseases, treatment consists of managing symptoms. Currently, drug therapy consists of antihistamines, corticosteroids, or the less effective leukotriene inhibitors and monoclonal anti-IgE antibodies, all of which have unwanted side effects. While the hygiene hypothesis continues to evolve and be debated,11-15 the use of probiotics to help manage allergic diseases continues to be a strong topic for clinical research.16-19 In particular, recent meta-analyses suggest that supplementation with a number of Lactobacilli species may reduce symptoms of some allergic diseases in children and adults.20-25
L-92 is a patented Lactobacilli strain26 that has been used in dietary supplements, fermented milk products, and other foods in Japan for decades. This review discusses its proposed mechanism of action based on laboratory and animal studies, as well as the results of clinical trials in subjects with allergic diseases.
Antiallergy Activity Interaction
After exposure to an antigen, antigen-presenting cells (macrophages, dendritic cells, Langerhans cells, and B-lymphocytes) process the antigen and present fragments to Th cells. These Th cells can further differentiate based on a complex interaction that depends on the type of antigen, the cytokines produced, T cell receptor signal strength, and the reciprocal feedback loop between Th2 and Th2 cells.27,28 Th1 cells respond to viral and some bacterial and protozoal infections, as well as malignant cells, and are necessary for innate and adaptive immunity. Th1 cells secrete the cytokines IFN-γ IL-2, and TNF-α.4,5 Mediating the humoral immune response, Th2 cells respond to extracellular parasites, bacteria, allergens, and toxins in the tissues where they are encountered, such as the skin, lungs, and gut.4,5,27,29 Activated Th2 cells produce cytokines like IL-4, IL-5, and IL-13 and are responsible for IgE antibody production by B cells to release histamine and leukotrienes from mast cells.4 Following activation by an allergen, naïve T cells preferentially differentiate into Th2 cells, thus increasing IgE production and resulting in common allergy symptoms.4,30
The various effects of Lactobacillus acidophilus strain L-92 on multiple immune response pathways appear to converge into one end result: counterregulation of type 2 helper cell (Th2)‒skewed immunity and the subsequent reduction in Th2-mediated allergic responses.
Increased serum IgE is a known risk factor for allergic response.31-33 The IgE-lowering effect of Lactobacilli was investigated by feeding milk cultured with 11 different Lactobacilli species/strains on serum ovalbumin (OVA)-IgE, total IgE, and total IgG levels in OVA-specific IgE-elevated mice. Eight of the samples significantly reduced the OVA-IgE levels compared to the control. The most significant decreases were observed in mice fed L fermentum CP34 and L acidophilus L-92. In addition, these 2 Lactobacilli strains had a higher recovery (calculated as ratio percentage of the counts obtained to the total ingested counts) in the mice's gastrointestinal (GI) tracts, confirming that adhesion in the GI tract may be important for exerting its immunomodulating activity.34 A lowering of OVA-specific IgE was also observed when heat-killed L-92 were administered to IgE-elevated mice.35,36
Mechanisms of Action
The induction of a Th1-biased immune response by L-92 may be explained by various mechanisms occurring within the immune network. One proposed mechanism is L-92’s influence on dendritic cells, a type of antigen-presenting cell found in tissues that are in contact with the external environment, such as the epithelial lining. Dendritic cells naturally produce the cytokine IL-12, which skews naïve T cells toward Th1 polarization. L-92 has been shown to stimulate IL-12 production from dendritic cells, inducing generation of Th1 cells and thus suppressing Th2 cell response. These in vitro and in vivo studies with L-92 also indicate that it inhibits the proliferation of antigen-stimulated CD4+ T cells and induces apoptosis of activated antigen-stimulated T cells, also through modulation of dendritic cell function, both of which regulate T cell homeostasis.37 Other possible mechanisms include regulation of Th1 and Th2 cytokines and activation of regulatory T (Treg) cells, a subtype of T cells whose purpose is to keep the immune response in check by preventing excessive reactions. In a mouse model, oral administration of L-92 was shown to regulate both Th1 and Th2 cytokine responses in favor of a Th1 response and induce transforming growth factor-β (TGF-β) production in dendritic cells of Peyer’s patches, small masses of lymphatic tissue, in the intestines. TGF-β is known to be associated with activation of Treg cells. These data suggest that L-92 may have an immunomodulating effect by Treg cells via TGF-β activity.34 It has also been demonstrated that the surface layer protein A (SlpA) has considerable adhesive activity and may be the protein that induces the IL-12 release from the dendritic cells.38 It has also been suggested that the adhesion of SlpA may aid in the communication between L-92 and the host via changes in gene expression.39
Additional mechanistic detail emerged from a recent study investigating the immunomodulatory response of macrophage-like THP-1 cells following cocultivation with L-92. THP-1 cells are a human monocytic cell line derived from an acute monocytic leukemia patient used as model for the study of monocyte-macrophage differentiation.40 In addition to an elevation of Th1-type cytokines, transcriptome analysis revealed that L-92 activated expression of a number of immunomodulatory genes. After 4 hours (early phase response), L-92 treatment upregulated transcription regulator genes and genes encoding chemokines and cytokines, all of which are associated with the MAPK signaling pathway and the NOD-like receptor signaling pathway. MAPK pathways control T cell development and differentiation, and the NOD-like receptors play a key role in regulation of innate immune response. After 24 hours (late phase response), transmembrane receptor and transcription regulator genes in the Toll-like receptor (TLR) signaling pathway were upregulated.41 TLRs are present on the surface of dendritic cells and are an important link between innate and adaptive immunity, producing IL-12 and IL-18, which in turn signal naive T-cells to mature into Th1 cells.
The various effects of L-92 on multiple immune response pathways appear to converge into one end result: counterregulation of Th2-skewed immunity and the subsequent reduction in Th2-mediated allergic responses. Clinical studies with L-92 for variety of allergic diseases provide further evidence for its use in their treatment.
According to the World Allergy Organization (WAO), allergic rhinitis, the IgE-mediated inflammation of the nasal mucosa, affects between 10% and 30% of the population.1 In the United States, allergic rhinitis (often called hay fever) affects approximately 50 million people, with almost 40% of children being affected.42 In a randomized, double-blind, placebo-controlled study, supplementation with heat-treated L-92-fermented milk in subjects with perennial allergic rhinitis resulted in statistically significant improvement of nasal symptom-medication scores. Ocular symptom-medication score (SMS) of patients in the L-92 intervention group tended to improve compared with those in the placebo group. In addition, clear decreases in the scores of swelling and color of the nasal mucosa were observed in the L-92 intervention group at 6 and 8 weeks. However, no effect was seen in the Th1/Th2 balance between the 2 groups.43
Seasonal allergic rhinitis occurs in spring, summer, and early fall. The most common allergy triggers are to pollens from trees, grasses, and weeds. In Japan, the Japanese cedar pollinosis is a serious health issue. Two placebo-controlled, single-blind studies were carried out during Japanese cedar pollination season to determine the effect of L-92 on the symptoms of Japanese cedar pollen allergy. Volunteers drank heat-treated milk fermented with L-92 per day for 6 weeks (study 1) and for 10 weeks (study 2). A significant improvement of the SMS was observed in study 1 and of the score of “distress of life” in study 2, although little difference was observed in the Th1/Th2 ratio between the 2 groups in both studies. No significant difference was observed in the scores for sneezing, runny nose, stuffy nose, itchy eyes, watery eyes, and nasal symptom‒medication score.44
Atopic dermatitis (AD) affects 8.7% to 18.1% of all infants and children.45 Disease onset is usually before 5 years of age in the majority of patients, and these young children may develop airway allergy such as asthma or allergic rhinitis later in life.46 A preliminary case study and a double-blind, placebo-controlled study that evaluated the effects of L-92 on symptoms of AD in children revealed that orally administered L-92 significantly ameliorated the symptoms. In both studies, children with moderate to severe AD symptoms received L-92 (in the form of heat-treated L-92 or a fermented milk containing viable L-92) once a day over a period of 8 weeks. Fermented milk is believed to contain microbes that possess the enzyme that is necessary to digest lactose, eliminating or reducing any symptoms related to lactose intolerance.47 Symptoms of AD were measured by the Atopic Dermatitis Area and Severity Index (ADASI) scoring system and by “itching score” as assessed by the patient and their parents. The primary outcome was the SMS, calculated as the sum of ADASI and the medication score, which was used to correct for effect of any topically applied corticosteroids. In addition, serum concentrations of thymus and activated-related chemokine (TARC), a marker of Th2 activation, were significantly lower in treatment group, indicating that L-92 altered the Th1/Th2 balance.48 This study confirms previous research in which L-92 inhibited AD-like skin lesions and symptoms such as scratching and swelling in allergy-induced mice. The treated mice also exhibited lower levels of mast cells, eosinophils, and Th1/Th2 cytokine expression.36
L-92 was also the topic of a similar double-blind, randomized, placebo-controlled clinical trial with adults with AD. Forty-nine patients were randomly allocated either 20.7 mg per day heat-killed L-92 in tablet form or a placebo. Clinical conditions of AD were evaluated by experienced dermatologists using the SCORing AD (SCORAD) index at baseline and after 4 and 8 weeks. Blood levels of eosinophils, serum IgE, several cytokines, lactate dehydrogenase, and TARC were also monitored in order to reflect AD progression. After 8 weeks, the treatment group had lower SCORAD scores than controls (P=0.002), decreased eosinophil count (P=0.03), and increased ratios of change for serum TGF-β (P=0.03). In addition, ratios of change for serum TGF-β rose significantly in patients showing mitigated symptoms after L-92 treatment (P=004).49 This study provides clinical evidence supporting the idea that one mechanism that L-92 induces Th1 dominance through is Treg cells via TGF-β activity as seen previously in an animal model.
L-92 may be able to reduce some symptoms of allergic disease. Current research proposes a number of pathways within the immune network to help support Th1/Th2 immunobalance, including induction of apoptosis of Th2 cells, modulation of dendritic function, regulation of Th1 and Th2 cytokines, activation of Treg cells, and upregulation of immunomodulatory genes. Clinical evidence supports the conclusion that L-92 may reduce some symptoms of AD, perennial allergic rhinitis, and pollen allergies. Recent research in a mouse model also suggests the L-92 may provide protective effects against influenza virus infection, demonstrating other potential use as an immune adjuvant.50
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