Surface IgA and Fc-alpha receptors on human alveolar macrophages from normal subjects and from patients with sarcoidosis.

Human alveolar macrophages (AM) obtained by bronchoalveolar lavage (BAL) were found to bear cytophilic IgA and Fc alpha-receptors (Fc alpha R) on their surface. The cytophilic IgA belongs to the IgA1 subclass, but unoccupied receptors can be saturated with either IgA1 or IgA2 molecules. Although both polymeric and monomeric forms could attach, binding was about 5-fold greater for the polymers. Both cytophilic IgA and Fc alpha R are sensitive to trypsin and disappear after 18 h of AM culture. An increase in cytophilic IgA was observed on AM from untreated patients with pulmonary sarcoidosis, but not on AM from steroid-treated patients. A significant correlation was found between IgA levels in BAL and the percentage of AM with cytophilic IgA in normal subjects and in steroid-treated sarcoid patients. However, no such relationship was seen among untreated patients. These data suggest that multiple factors may modulate AM surface receptors for IgA. Inflammatory events occurring in the lungs could alter receptor expression and perhaps be of significance in the immunophysiopathology of certain pulmonary diseases.

Massive plasma cell infiltration of the digestive tract. Secretory component as the rate-limiting factor of immunoglobulin secretion in external fluids.

A 29-yr-old Tunisian man had a clinical immunoproliferative small intestinal disease, different from alpha-chain disease. Serum contained 52.5 mg/ml of polymeric immunoglobulin A (IgA). Immunohistochemistry revealed a massive diffuse polyclonal IgA (99%)-plasma cell infiltration in the small bowel mucosa, with a smaller increase of IgA-producing cells in gastric and colonic mucosae. Secretory IgA levels were normal in jejunal and bronchoalveolar secretions. However, both fluids contained polymeric IgA devoid of secretory component, and free secretory component was absent. This suggests that secretory component was the limiting factor in transport of IgA in the secretions. A relative deficiency in secretory component, as compared with the huge supply of polymeric IgA, may have limited the secretory component-mediated active transport of IgA into secretions. This resulted in the appearance of high levels of polymeric IgA, unlinked to secretory component, both in serum and in the jejunal and bronchoalveolar fluids.

Antiproteases are increased in bronchoalveolar lavage in interstitial lung disease.

The present study evaluates different cellular and soluble components in the bronchoalveolar lavage (BAL) from patients with interstitial lung disease. We observed an increased T4/T8 lymphocyte ratio in BAL but not in blood from 24 patients with active pulmonary sarcoidosis compared to sixteen normal individuals and to eleven patients with inactive pulmonary sarcoidosis. Seven patients with hypersensitivity pneumonitis had a normal T4/T8 ratio. In the active sarcoidosis and hypersensitivity pneumonitis groups, alpha 1-Protease Inhibitor (alpha 1 PI) in BAL is significantly higher than in the normal group and a significant correlation between the two antiproteases (alpha 2-macroglobulin and alpha 1 PI) is observed. These data demonstrate that antiprotease levels (alpha 1 PI and alpha 2 M) are increased in the lower respiratory tract of patients with interstitial lung disease and that among cellular and soluble components of BAL, alpha 2 M represents a sensitive marker of the alveolitis.

A polymeric IgA response in serum can be produced by parenteral immunization.

The magnitude and the kinetics of the serum-specific polymeric (p-) and monomeric (m-) IgA antibody responses were analysed following parenteral stimulation with tetanus toxoid (TT) vaccine in 10 volunteers, 5-20 years after a previous boost. A rapid marked serum IgA antibody response involving both the monomeric and polymeric components of IgA was observed: m-IgA and p-IgA antibodies reached a peak of serum activity at about 11 days, around 6 days before the peak of IgG antibody activity. At the peak of the IgA response, p-IgA accounted for approximately half of the anti-TT activity (median 54%, 25-79%). However, p-IgA antibodies rapidly disappeared from serum over a few weeks, whereas the serum m-IgA antibody response was maintained over a prolonged period of time. For one subject out of five, anti-TT IgA were also detected in saliva with a peak of activity earlier than in serum. Calculation of the albumin relative coefficient of excretion for anti-TT IgA in this saliva suggested a local synthesis of these antibodies. The present study indicates that a polymeric IgA antibody response in serum can be produced by parenteral immunization in primed individuals, and it raises the question of the mechanisms that control polymeric versus monomeric IgA production.

Kinetics of anti-Campylobacter jejuni monomeric and polymeric immunoglobulin A1 and A2 responses in serum during acute enteritis.

The intensity and kinetics of the serum polymeric and monomeric immunoglobulin A1 (IgA1) and IgA2 antibody responses to Campylobacter jejuni were analyzed. A rapid and marked serum IgA antibody response involving both the monomeric and polymeric components of IgA was observed after C. jejuni infections. IgA antibodies reached a peak of activity in serum during week 2 after the first symptoms of enteritis, about 10 days before the peak of IgG activity. Polymeric IgA accounted for most of the anti-C. jejuni activity at the peak of the IgA response (median, 90%; range, 44 to 98%) but rapidly disappeared from serum over a few weeks. In contrast, the serum monomeric IgA antibody response was low and was maintained over a prolonged period of time. Anti-C. jejuni IgA detected in the serum of healthy blood donors was mainly monomeric (median, 83%; range, 17 to 94%). In both the patients and the positive controls, IgA1 was the predominant (greater than 85%) subclass involved, even when the IgA antibody response was mainly polymeric. Our results suggest that polymeric IgA antibody responses are linked to a strong or persisting antigenic stimulation or both. Polymeric IgA antibodies appear to be a potential marker of acute C. jejuni infections, and their determination could provide a useful tool for the serological diagnosis of recent C. jejuni infections.

IgA-induced chemokinesis of human polymorphonuclear neutrophils: requirement of their Fc-alpha receptor.

The influence of purified human immunoglobulins on the migration of human neutrophils (PMN) was measured in a 48-well micro chemotaxis chamber, with results expressed as percentages of maximal formyl-methionyl-leucyl-phenylalanine (FMLP)-stimulated chemotaxis. Both monomeric and polymeric IgA, of both subclasses, in monoclonal and polyclonal form, as well as secretory IgA and Fc-alpha, but not Fab-alpha fragments, enhanced PMN migration when present either in the lower or in both compartments of the chamber (chemokinesis) at concns as low as 0.1 mg/ml. IgM and IgE had no such effect. In contrast, IgG was chemotactic at low concn (0.1 mg/ml). Both monomeric and polymeric IgA decreased the maximally induced FMLP-chemotaxis, but IgA increased chemotaxis induced by suboptimal levels of FMLP. Binding of 3[H]-FMLP to PMN was not affected. Cytofluorographic analysis revealed that, under the conditions of the assay, IgA did bind to 93% of PMN. Thus, the various forms of IgA have a dual effect on human PMN mobility: (1) increase PMN random migration (chemokinesis); and (2) decrease the maximal FMLP-induced chemotaxis. Our data support the requirement of binding of IgA to the Fc-alpha receptor of PMN for expression of these activities. This effect of IgA on PMN mobility may be relevant in IgA deficiency states.

Intravascular and mucosal immunoglobulin A: two separate but related systems of immune defense?

Immunoglobulin A has long been referred to as the antibody of mucosal secretions. However, in the last few years there has been increased interest in serum IgA, in factors that regulate the various forms of IgA produced, and in the relationship between serum and mucosal IgA. Recent data indicate that in humans, the mucosal surfaces are neither the source nor the destination of serum IgA. By estimating the amounts of IgA produced at various sites throughout the body, we have shown that in humans more IgA is synthesized and secreted each day than IgG and IgM combined; about one third of this IgA is secreted directly into the vascular compartment and never reaches the mucosal surfaces. We also consider a possible role for serum IgA as the "discreet housekeeper," the relationship between cells that produce IgA in the serum and IgA in secretions, and factors that influence the various forms of IgA produced.

Characteristics of serum IgA and liver IgA deposits in alcoholic liver disease.

Patients with alcoholic liver disease frequently reveal an increase in IgA serum concentration and IgA deposits in a continuous pattern along hepatic sinusoids. We investigated whether the hepatic IgA deposits are a passive reflection of changes in concentration or composition of IgA in the circulation, or represent a distinct effect of alcohol on the liver. Forty-one patients with alcoholic liver disease (daily alcohol intake at least 50 gm for more than five consecutive years) were compared with 41 patients with nonalcoholic liver disease. Patients in both groups were matched for serum IgA and histopathological changes in the liver biopsy. IgA deposits in the liver were found in 78% of the alcoholic patients and in 12% of the nonalcoholic patients. The presence of deposits was not related to histopathological changes in the liver or to the serum IgA concentration. In serum IgA subclass distribution, alcoholic patients differed from nonalcoholic patients by a slight but significant shift to IgA2; in contrast, the hepatic IgA deposits in alcoholic patients were almost of the IgA1 subclass. Serum secretory component (which is an equivalent of serum secretory IgA) was elevated in both alcoholic and nonalcoholic patients; patients with a liver biopsy revealing hepatitis showed the highest level. In contrast, the hepatic deposits did not contain secretory component. We conclude that the continuous deposits of IgA along liver sinusoids are not a passive reflection of changes in concentration or composition of circulating IgA, but may represent a distinct effect of alcohol on the liver related to the role of this organ in IgA metabolism.

Characteristics of IgA deposits in liver and skin of patients with liver disease.

The presence of IgA deposits in a continuous pattern along hepatic sinusoids is a specific entity for alcoholic liver disease. In superficial skin blood vessels of patients with liver disease, IgA deposits can occur. The authors characterized the deposits for IgA-subclass epitope expression and for macromolecular configuration (assessment of [hidden] J-chain determinants and of secretory component-binding capacity). A variety of monoclonal anti-IgA-subclass reagents were applied, which proved to be specific in control experiments on blastoid cells generated by pokeweed mitogen stimulation of blood mononuclear cells and frozen tissue sections of normal jejunum. IgA1 is the major component in IgA deposits in liver (n = 83) and skin (n = 31) of patients with liver disease. Macromolecular IgA is detectable in only one-fifth of the cases. The authors' data do not indicate that hepatic IgA deposits in liver disease are of gastrointestinal origin. Out of the circulating IgA pool, IgA1 appears to be most capable of being deposited in tissue.

Altered patterns of secretion of monomeric IgA and IgA subclass 1 by intestinal mononuclear cells in inflammatory bowel disease.

Intestinal mononuclear cells (MNC) from patients with inflammatory bowel disease (IBD) demonstrated altered patterns of spontaneous secretion of immunoglobulin A (IgA). Control intestinal MNC had markedly high spontaneous secretion of IgA compared to IBD intestinal MNC. Control intestinal MNC secreted predominantly dimeric IgA (only 31% monomeric IgA), whereas IBD intestinal MNC secreted increased amounts (43%-53%) of monomeric IgA. Control intestinal MNC secreted 61% IgA subclass 1 (IgA1), whereas IBD intestinal MNC secreted 71%-74% IgA1. Intestinal MNC from involved portions of resected specimens secreted more of both monomeric IgA and IgA1 than MNC from uninvolved areas of the same bowel. Therefore, intestinal MNC from involved IBD intestinal specimens secrete less total IgA but high percentages of monomeric IgA and IgA1 compared to control intestinal MNC. This could be caused by increased homing of monomeric IgA- and IgA1-producing cells into involved intestine, or the in situ proliferation of monomeric IgA and IgA1 precursor cells resulting from immunoregulatory alterations. These observations may represent the normal mucosal IgA immune response to infectious agents or inducing factors of either a primary or a secondary nature.

Monoclonal antibodies against isotypic and isoallotypic determinants of human IgA1 and IgA2: fine specificities and binding properties.

We have analysed and compared the fine specificity and behavior in various immunoassays of 10 mouse monoclonal antibodies, from three independent laboratories, directed against IgA1, IgA2 or non-IgA2m(2). The following observations were made. (1) Although all of the monoclonal antibodies were specific for a particular IgA subclass or isoallotype in a radioimmunoassay, three of them were not specific when tested in indirect immunofluorescence on plasma cells derived from pokeweed-activated peripheral blood lymphocytes. In this highly sensitive system, contrary to direct immunofluorescence previously performed using formalin-fixed lymphoid tissue, the anti-IgA1 69.114 reacted with some of the IgA2 plasma cells, the anti-IgA2 DLDB7 reacted with some of the IgA1 plasma cells and the anti-IgA2 16.512 dimly reacted with all IgM plasma cells. (2) Among the eight anti-IgA subclass antibodies, seven were directed against the CH2 domain of IgA whereas the anti-IgA1 1-155-1 recognised an epitope destroyed by Streptococcus sanguis IgA1 protease and localised in the hinge region of IgA1. The two anti-isoallotype antibodies were directed against epitope(s) probably localised in the 65 C-terminal amino acid residues of the alpha-CH3 domain. All of the 10 antibodies were able to react with endogeneously produced surface IgA on B-cells. (3) Using monoclonal anti-IgA subclass antibodies in radioimmunoassay may be hazardous in the absence of knowledge of their affinity constants and of careful control experiments: some of the antibodies were not sensitive in radioimmunoassays designed to measure the serum titer of specific IgA1 and IgA2 antibodies. Moreover, major differences were observed between the different monoclonal reagents with respect to the influence of the size of IgA on a solid-phase sandwich radioimmunoassay. While three of the anti-IgA1 underestimated dimeric IgA relative to monomeric IgA, the fourth anti-IgA1 and all the anti-IgA2 overestimated dimeric IgA relative to monomeric IgA, by a factor sometimes close to 7.

Alpha-2-macroglobulin, monomeric and polymeric immunoglobulin A, and immunoglobulin M in bronchoalveolar lavage.

The concentrations of alpha 2-macroglobulin (alpha 2M), IgM, and the various molecular forms of IgA were measured in unconcentrated bronchoalveolar lavage (BAL) of normal subjects and in that of patients with interstitial lung disease. In BAL of control subjects, as previously observed in other external secretions, orosomucoid-coefficient of excretion relative to albumin (RCE) = 1.1 (albumin RCE = 1)-IgG (RCE = 0.7 in nonsmokers), and alpha 2M (RCE = 0.04) appeared to be secreted mainly by seepage from plasma according to molecular size. The secretion of p-IgA (RCE = 22), IgM (RCE = 0.09), and transferrin (RCE = 1.2) was selective, suggesting either local lung synthesis of these components or their active transepithelial transport. Concentrations of p-IgA, alpha 2M, and IgM in BAL displayed RCE at least 10 times lower than in other external secretions, reflecting the unsignificant local synthesis of these components in alveolar septa. In interstitial lung diseases, including sarcoidosis, hypersensitivity pneumonitis, and other lung fibroses, all protein concentrations in BAL were raised. Increased seepage of plasma proteins across the blood-gas barrier accounted for the elevation of orosomucoid and p-IgA (RCE unchanged). It probably accounted for the appearance in BAL of a characteristic peak of serum type dimeric IgA unbound to secretory component (SC), for the reduced percentage of free SC (5% versus 27% in control subjects), and for part of the increased percentage of m-IgA (52% versus 28% in control subjects). Contribution of local synthesis, presumably by cells infiltrating the alveolar tissue, was indirectly demonstrated for m-IgA and IgG, which were selectively secreted, more than 2-fold greater than albumin.(ABSTRACT TRUNCATED AT 250 WORDS)

Gall bladder: the predominant source of bile IgA in man?

The sedimentation profiles of IgA and Secretory Component (SC) and the concentrations of IgA, IgG, IgM, SC and albumin were evaluated after an overnight fast in gall bladder bile of six adult subjects without hepatobiliary disease. The sedimentation profiles differed from those previously obtained in hepatic bile in three ways: gall bladder bile contained a greater percentage of free-SC, a greater percentage of polymeric-IgA (p-IgA), and a major peak of 14 to 19 S p-IgA associated to SC. In contrast to hepatic bile in which IgG is the predominant Ig, IgA clearly was the predominant Ig in gall-bladder bile, its concentration averaging 92 micrograms/ml. Relative-to-albumin coefficients of excretion of proteins in gall bladder bile averaged 0.99 for IgG, 8.6 for monomeric IgA, 196 for p-IgA and 31 for IgM, indicating that there was a selective excretion of IgA and IgM into gall bladder bile. As compared to hepatic bile, the enrichment of gall bladder bile with IgA and IgM was respectively 6.5 and 11.5 times greater than with IgG. These results suggest that quite a significant amount of p-IgA could have been added to bile during its storage in the gall bladder which should therefore be regarded as the predominant source of bile IgA in humans.

Hepatobiliary transport of plasma IgA in the mouse: contribution to clearance of intravascular IgA.

Labeled monomeric and polymeric (pIgA) mouse monoclonal IgA were injected intravenously into mice which were either sequentially bled for plasma turnover studies of IgA, or cannulated at their common bile duct, with excluded gallbladder, for quantitation of plasma-to-bile transport of pIgA. Our data show that mice do display a relatively high rate of biliary transport of plasma pIgA (22-28% of the injected 125I-labeled pIgA over 3 h), which accounts for approximately 90% of the total amount of pIgA (8.8 mg/kg/day) daily delivered by hepatic bile into the duodenal fluid of this species. However, in mice the absolute biliary output of pIgA does not exceed that of IgG (9.5 mg/kg/day) and the kinetics of the hepatobiliary transport of plasma pIgA appear to be slower than in the rat. Furthermore, as plasma survival studies of 125I-labeled pIgA yielded a plasma turnover of pIgA averaging 20.6 mg/kg/day, it can be approximated that the hepatobiliary pathway contributes for only 38% to the elimination of intravascular pIgA from mouse plasma, a figure to be compared to 89.8% in the rat and approximately 8.9% in man. We conclude that internal catabolism plays a dominant role in the clearance of intravascular pIgA in the mouse which appears as a model intermediate between rats and humans. Supporting this conclusion, serum pIgA two days after common bile duct ligation in 6 mice was increased by 2.5-fold vs. greater than 14-fold in ligated rats and 1.1-fold in humans with complete biliary obstruction.