Origin, distribution and differentiation of IgA-producing cells

Role of antibiotics and fungal microbiota in driving pulmonary allergic responses

Over the past four decades, there has been a significant increase in allergy and asthma in westernized countries, which correlates with alterations in fecal microbiota (microflora) and widespread use of antibiotics (the "hygiene hypothesis"). Antibiotics also lead to overgrowth of the yeast Candida albicans, which can secrete potent prostaglandin-like immune response modulators. We have developed a mouse model of antibiotic-induced microbiota disruption that includes stable increases in gastrointestinal (GI) enteric bacteria and GI Candida levels with no introduction of microbes into the lungs. Mice are treated for 5 days with cefoperazone in the drinking water, followed by a single oral gavage of C. albicans. This results in alterations of GI bacterial populations and increased yeast numbers in the GI microbiota for at least 2 to 3 weeks and can drive the development of a CD4 T-cell-mediated allergic airway response to subsequent mold spore (Aspergillus fumigatus) exposure in immunocompetent mice without previous systemic antigen priming. The allergic response in the lungs is characterized by increased levels of eosinophils, mast cells, interleukin-5 (IL-5), IL-13, gamma interferon, immunoglobulin E, and mucus-secreting cells. In the absence of antibiotics, mice exposed to Aspergillus spores do not develop an allergic response in the airways. This study provides the first experimental evidence to support a role for antibiotics and fungal microbiota in promoting the development of allergic airway disease. In addition, these studies also highlight the concept that events in distal mucosal sites such as the GI tract can play an important role in regulating immune responses in the lungs.

The common mucosal immune system and current strategies for induction of immune responses in external secretions

The selective induction of antibodies in external secretions is desirable for the prevention of various systemic as well as predominantly mucosa-restricted infections. An enormous surface area of mucosal membranes is protected primarily by antibodies that belong, in many species, to the IgA isotype. Such antibodies are produced locally by large numbers of IgA-containing plasma cells distributed in subepithelial spaces of mucosal membranes and in the stroma of secretory glands. In humans and in some animal species, plasma-derived IgA antibodies do not enter external secretions in significant quantities and systemically administered preformed IgA antibodies would be of little use for passive immunization. Systemic administration of microbial antigens may boost an effective S-IgA immune response only in a situation whereby an immunized individual had previously encountered the same antigen by the mucosal route. Local injection of antigen in the vicinity of secretory glands is usually accompanied by an undesirable concomitant systemic response and frequently requires the addition of adjuvants that are unacceptable for administration in humans. Immunization routes that involve ingestion or possibly inhalation of antigens lead to the induction of not only local but also generalized immune responses manifested by the parallel appearance of S-Iga antibodies to ingested or inhaled antigens in secretions of glands distant from the site of immunization. Based on extensive studies in animal models as well as in humans, convincing evidence is available that antigen-sensitized and IgA-committed precursors of plasma cells from GALT are disseminated to the gut, other mucosa-associated tissues, and exocrine glands. However, due to the limited absorption of desired antigens from the gut lumen of orally immunized individuals, repeated large doses of antigens are required for an effective S-IgA response. Novel antigen delivery systems for the stimulation of such responses are currently being examined in several laboratories. Live attenuated or genetically manipulated bacteria expressing other microbial antigens have also been used for selective colonization of gut-associated lymphoid tissues. Unique antigen packaging and the use of adjuvants suitable for oral administration hold promise for an efficient antigen delivery to critical tissues in the intestine and deserve extensive exploration. The oral immunization route appears to have many advantages over systemic immunization.(ABSTRACT TRUNCATED AT 400 WORDS)

Postnatal development of bronchus-associated lymphoid tissue (BALT) in the rat, Rattus norvegicus

The pattern of development of bronchus-associated lymphoid tissue (BALT) in specified-pathogen-free and conventional (non-barrier maintained) rats over the initial 4 weeks of life appeared to be similar. BALT first appeared around the 2nd week of life and increased in amount over the following 2 weeks. Overlying large nodules of BALT the bronchial epithelium becomes infiltrated by lymphocytes to form a lymphoepithelium. This transformation occurs earlier in conventional rats, possibly because of the differing antigen levels to which they are exposed.

Selective induction of an immune response in human external secretions by ingestion of bacterial antigen

Ingestion of capsules which contained killed Streptococcus mutans by four healthy human subjects led to the appearance of specific antibodies in external secretions. Salivary and lacrymal antibodies were detected within 1 wk of ingestion and continued to increase throughout a 14-day immunization period, with a gradual decline during the 2 ensuing months. A second period of immunization resulted in a pronounced increase of specific antibody levels which occurred earlier than in the primary immunization period and reached peak levels by day 10. No change was detected in serum antibody levels throughout either immunization period. The antibody activity in all secretions was associated with the immunoglobulin A class, as determined by immunochemical analyses. These data indicate that ingestion of bacterial antigens selectively stimulates the immune response in secretions.