Increased rates of polymeric IgA synthesis by circulating lymphoid cells in IgA mesangial glomerulonephritis.

Recently we have described the existence of high levels of polymeric IgA, partially as immune complexes, in the serum and kidney from patients with IgA mesangial glomerulonephritis. As these patients often have macroscopic haematuria, following upper respiratory tract infections, our working hypothesis in this paper was that circulating lymphocytes from secretory tissues after viral stimulus could produce in these patients a large amount of polymeric IgA. To test it, peripheral blood lymphocytes (PBL) from patients and controls were cultured for seven days in the presence or absence of pokeweed mitogen (PWM). In cell culture supernatants immunoglobulin synthesis was measured by RIA and the proportion of polymeric and monomeric IgA was determined on Ultrogel Ac A22 column. There was no difference in spontaneous production of immunoglobulins between patients and controls. On the contrary, the IgA synthetized by PWM-stimulated PBL was significantly higher in patients than in controls. The percentages of IgA with molecular weight between 600,000 and 250,000 after supernate fractionation were significantly higher in patients than in controls. The true nature of polymeric IgA was confirmed by their ability to bind secretory component, the existence of covalent structures, and the decrease of the larger forms of IgA after reduction and alkylation. The percentage of IgA producing cells binding secretory component was significantly higher in patients than in controls (69 +/- 21 versus 44 +/- 27) after seven days of culture. IgM and IgG produced in patient culture were similar to controls. These results show that mitogen stimulated PBL from patients with Berger's disease synthetized a large amount of true polymeric IgA. It is suggested that a similar situation could occur in vivo after viral of other stimuli.     

Tracheal and bronchial polymeric immunoglobulin secretory immune system (PISIS) development in a porcine model

Polymeric immunoglobulins (pIgs) mucosal secretion is mediated by the pIg secretory immune system (PISIS), which is composed of J-chain (JC) and antibody (IgM/IgA) producing cells (JC-AbPC), pIg receptor (pIgR) epithelial cell expression and the efficient release of secretory Igs (SIgs) to the mucosal lumen. A poor development or disturbances in this system may cause higher infection susceptibility, as observed in young and elderly people. In spite of this system's importance, few detailed studies regarding its development have been described in the lower respiratory tract of humans. Because the porcine model has been reported as an option for translational medicine to humans, we studied the tracheal and bronchial PISIS development in healthy, non-vaccinated, SPF, miniature Vietnamese pigs from birth to adulthood using immunohistochemistry and ELISAs. Our results demonstrated that pIgR was present at birth, and its expression increased with age. In contrast, JC-AbPC were low in neonatal pigs; however, colostrum was a source of IgM, SIgA, total IgA and IgG in respiratory secretions (trachea and bronchoalveolar lavages, nasal secretion and saliva) in piglets. JC-AbPC steadily increased in post-weaned, young and adult pigs, correlating with considerable increases in secretory and total Igs in the trachea and bronchi. These data suggest a compensatory role of maternal Igs at the respiratory mucosa in the absence of a structured PISIS before weaning. Furthermore, monomeric Igs (IgG and IgA) may also play an important role in respiratory protection and deserves a more thorough study.     

Decreased suppressor T cell activity in patients with hepatic cirrhosis (HC).

Hypergammaglobulinaemia (HGG) is frequently found in patients with hepatic cirrhosis (HC). Using an assay system of in vitro PWM-stimulated immunoglobulin (Ig) production, the amounts of IgG, IgA, and IgM produced by peripheral blood lymphocytes (PBL) from 15 HBs Ag-negative patients with HC and from 16 age-matched healthy subjects were quantitated by radioimmunoassay. We found that PBL from patients with HC produced significantly greater amounts of IgG (P less than 0.05) but not IgA or IgM than did those from control subjects. This increased IgG production by PBL from patients with HC was attributed to enhanced T helper activity and not to enhanced B cell function. We also searched for defects in naturally occurring suppressor T cell activity which is sensitive to irradiation. Irradiation-induced enhancement for IgG production was significantly lower in patients with HC compared with age-matched control subjects (P less than 0.01). Similarly, we examined the effect of Con A-induced suppressor T cells on the in vitro PWM-stimulated IgG production by allogeneic PBL and observed the decrease of Con A-induced suppressor T cell activity in patients with HC (P = 0.01). We conclude, therefore, that the increased serum levels of Ig, particularly IgG in patients with HC may result from in part on the basis of depressed ability of naturally occurring suppressor T cells or Con A-induced suppressor T cells to suppress Ig production.     

Immunohistochemical characterization of intracellular J-chain and binding site for secretory component (SC) in human immunoglobulin (Ig)-producing cells

J-chain staining of IgA- and IgM-producing immunocytes was significantly enhanced when tissue sections were pretreated with acid urea, apparently because molecular unfolding exposed concealed J-chains. This indicated substantial completion of the Ig polymers at the cytoplasmic level, which was verified by diffuse binding of SC in vitro to the cytoplasm of most J-chain-positive IgA and IgM cells. This process involved specific non-covalent forces which showed the same interrelation as that noted for isolated dimeric IgA and 19S IgM--the latter as well as IgM cells exhibiting stronger binding of SC than the IgA counterparts. Conversely, J-chain staining of IgD and IgG immunocytes was not enhanced by acid urea and these cells did not generally express affinity for SC; rare exceptions could apparently be ascribed to artifacts or dual isotype production including IgA or IgM polymers. Parallel demonstration of J-chain and SC binding seems to be the best available method for studies of polymer-producing immunocyte populations and offers the advantage of in situ evaluation of cell distribution in relation to morphology. The reliability of this approach was attested to by the fact that IgA immunocytes in all secretory tissues investigated (salivary, mammary and lacrimal glands; nasal and intestinal mucosae) expressed J-chain (87-97%) and SC affinity (84-87%) in comparable proportions, indicating that almost 90% of the cells were engaged mainly in dimer production. The observation that most IgD and 50-70% of the IgG immunocytes in secretory tissues expressed J-chain, has implications for the differentiation of B-cell clones homing to such sites. Conversely, IgG cells in extra-glandular tissues showed strikingly reduced J-chain production and such sites contained IgA immunocytes with heterogeneous expression of J-chain and SC affinity. Thus, in the extra-follicular area of palatine tonsils 70-80% of the IgA cells seemed to be pure monomer producers and the remainders apparently generated a mixed product. Most immunocytes in extra-glandular tissues may therefore belong to mature clones with completely or partially repressed J-chain synthesis.     

Phenotype characteristics of human B cells studied by Epstein-Barr virus infection. I. Immunoglobulin expression on human lymphoblastoid cells established from various lymphoid cells

Forty-seven lymphoblastoid cell lines were established from human fetal lymphoid tissues, cord blood lymphocytes (CBL) and adult peripheral blood lymphocytes (PBL) by Epstein-Barr virus (EBV) infection. Their surface immunoglobulin (sIg), intracytoplasmic immunoglobulin (cIg) expression, and immunoglobulin (Ig) content in the culture supernatant were tested. Expression of sIgM, sIgG and sIgA were predominant on fetus-derived cell lines, while sIgD was the most prominent on CBL-derived cells. Though cIg expression did not vary between cell lines of different origin, Ig content in the culture supernatant differed greatly. Fetus- and CBL-derived cells secreted IgM exclusively, but PBL-derived cells secreted not only IgM, but also IgG and IgA abundantly. These results indicate that the lymphoblastoid cells established by EBV infection reflect the Ig phenotype of the cell from which they originated.     

Vasoactive intestinal peptide stimulates immunoglobulin production and growth of human B cells.

The effect of vasoactive intestinal peptide (VIP) on human lymphoblastoid B cell lines and tonsil B cells was studied. VIP increased immunoglobulin production and proliferation by lymphoblastoid B cell line, GM-1056, in a dose-dependent manner. As little as 10(-12) M of VIP was effective, and higher concentrations of VIP induced an approximately five-fold increase in IgA production. Moreover, this enhancement was blocked by VIP antagonist. Similarly, VIP enhanced IgM and IgG production by other lymphoblastoid B cell lines, CBL and IM-9, respectively. In contrast to VIP, another neuropeptide substance P (SP) or somatostatin failed to enhance immunoglobulin production and thymidine uptake. VIP also enhanced IgA production and thymidine uptake by purified tonsil B cells. However, in contrast to B cell lines, VIP failed to enhance IgM and IgG production by tonsil B cells. SP or somatostatin failed to enhance immunoglobulin production or thymidine uptake by tonsil B cells. These results indicate that VIP acts as B cell stimulatory factor and that VIP may also have preferential effect on IgA production on tonsil B cells.     

Cell surface immunoglobulin μ and γ chains of human lymphoid cells are of higher apparent molecular weight than their secreted counterparts

Selected human lymphoma-derived and lymphoblastoid cell lines have been characterized and shown to be useful model systems for the expression of either cell surface Ig, or secretory Ig, or both simultaneously. Daudi and Raji cell lines were shown to express surface IgM with no secretion of IgM. The lymphoblastoid cell lines Tay-3 and RPMI 1788 are high-rate secretors of IgM. The lymphoma cell line BJAB synthesizes both cell surface IgM and secretory IgM. In the secreting cells, we have identified an intracellular μ chain with an apparent molecular weight approximately 2000 less than secreted μ chain. In cells synthesizing surface IgM, a surface μ chain has been identified which has an apparent mol. wt. of approximately 2000 more than secreted μ chain. The intracellular μ chain in these cells is indistinguishable in size from the mature surface μ chain; the Daudi cell line is exceptional in that surface deposition of the intracellular μ chain is preceded, or accompanied, by an increase in apparent mol. wt. The lymphoblastoid cell line Bec-11 synthesizes both cell surface IgG and secretory IgG. In Bec-11 cells, a surface form of μ chain, having a higher apparent mol. wt. than secreted γ chain, has been resolved. There is no detectable difference between L chains associated with any of the different forms of H chain. A biosynthetic relationship between the different forms of H chain is proposed.     

Molecular size heterogeneity of immunoglobulins in health and disease.

The molecular size of serum IgG, IgA and IgM in patients with a variety of monoclonal and polyclonal immune disorders has been determined by a sensitive immunoblotting technique. IgM, IgA and IgG3 paraproteins from patients with B cell lymphoproliferative disorders frequently polymerize with IgA paraproteins demonstrating two polymeric series, the basic unit of the more dominant series being monomeric IgA, and the second consists of a basic unit having a molecular mass of approximately 70 kD heavier than monomeric IgA. The molecular nature of this heavier IgA moiety was shown to be IgA covalently bound with a single molecule of serum albumin or alpha 1 antitrypsin and this moiety was also observed in small quantities in sera from healthy subjects. IgM paraproteins, particularly from patients with malignant lymphoproliferative disorders, consisted of varying proportions of decamers, pentamers and monomers together with other low molecular weight IgM oligomers. Paraproteins from patients with benign conditions showed less tendency to exist in multiple molecular weight forms. Serum immunoglobulins from patients with polyclonal immune disorder also showed molecular sized heterogeneity. Significantly increased levels of dimeric IgA were observed in patients with alcoholic cirrhosis and Felty's syndrome, while low molecular weight IgM was commonly seen in patients with autoimmune disorders. In these latter disorders monomeric IgM correlated significantly with the serum IgM level suggesting a disorder of assembly of the IgM subunits during an ongoing IgM immune response. We have demonstrated considerable molecular size heterogeneity of serum immunoglobulins both in health and disease and have indicated some possible clinical associations.     

Induction of the receptor for the Fc portion of IgA by secretory IgA on human T cell lines and T cell clones

Human colostral secretory IgA (SIgA; predominantly present in dimeric of polymeric forms) induces receptors for the Fc portion of IgA (Fc alpha R) on cloned and noncloned human T cell lines. The binding of SIgA to its FcR was isotype specific, since it was not inhibited by IgG or IgM. Binding of SIgA was also not affected by ovalbumin asialoglycoprotein. In addition, SIgA blocked the binding of directly fluorescein isothiocyanate-labeled SIgA in a dose-dependent fashion, whereas IgG and IgM were ineffective, confirming the specificity of the binding. Expression of Fc alpha R was specifically induced by SIgA, whereas serum IgA (predominantly present in monomeric form) had no effect. In addition, IgG, IgM and IgE were ineffective. This induction of Fc alpha R by SIgA was dose dependent. Optimal induction was observed at concentrations of 500 micrograms/ml after incubation times of 48 h. Fc alpha R were predominantly induced on T cell lines and T cell clones derived from tonsils. T cell lines and T cell clones established from peripheral blood could only occasionally be induced to express Fc alpha R. Induction of Fc alpha R expression was obtained both with CD4+ and CD8+ T cell clones. Fc alpha R were readily induced on T cell clones tested up to 6 days after activation by alloantigen. T cell clones tested 10-12 days after alloantigen activation failed to respond to SIgA. These results indicate that the inducibility of Fc alpha R is related to the activation stage of the T cell clones.     

Distribution of Ig Classes and IgG Subclasses among Human B Cells Activated by Nocardia opaca-Delipidated Cell Mitogen or by Pokeweed Mitogen

The relative proportions of cells synthesizing the three major Ig classes or one of the four IgG subclasses in cultures stimulated with pokeweed mitogen (PWM) or Nocardia-delipidated cell mitogen (NDCM) were investigated. In cultures of human peripheral blood mononuclear cells (PB MNC) stimulated with PWM, the number of IgG-containing cells (CC) was higher than the number of IgM-CC, and a substantial number of IgA-CC was found. Conversely, in NDCM-stimulated PB MNC cultures IgM-CC outnumbered IgG-CC and only few IgA-CC were detected. In those cultures, the removal of T cells resulted in an increase in the number of IgM-CC concomitant with a decrease in the number of IgG-CC. A substantial number of cells containing simultaneously IgG or IgA in addition to IgM could be found in PWM-stimulated cultures. These cells were virtually absent in NDCM-stimulated cultures. The relative proportions of IgG subclass-CC were IgG1-CC greater than IgG2-CC greater than IgG3-CC greater than or equal to IgG4-CC in PWM-stimulated and IgG2-CC greater than IgG1-CC greater than IgG3-CC greater than or equal to IgG4-CC in NDCM-stimulated cultures. The removal of T cells from NDCM-stimulated cultures did not result in major alteration of this distribution. The role of T cells and of the genomic order of the Igh-C genes in their phenotypic expression triggered in vitro by PBA is discussed.     

Prolonged and preferential production of polymeric immunoglobulin A in response to Streptococcus pneumoniae capsular polysaccharides.

Streptococcus pneumoniae is an invasive mucosal pathogen for which host defense is dependent on capsular polysaccharide-specific antibody. Capsule-specific immunoglobulin G (IgG), IgM, and IgA are produced following pneumococcal vaccination and infection. Serum IgA has two molecular forms, polymeric and monomeric. These forms may modulate the avidity of antigen binding and evolve over time as the immune response matures. Therefore, we sequentially characterized the molecular forms of serum IgA to three serotypes of pneumococcal capsular polysaccharides (types 8, 12F, and 14) after pneumococcal vaccination and after natural infection with type 14 S. pneumoniae. Although typically the form of IgA in antigen-specific systemic responses to protein antigens is predominantly polymeric in sera of patients shortly after exposure and shifts to the monomeric form in sera obtained several weeks later, the form of IgA in response to each pneumococcal capsular polysaccharide remained predominantly polymeric 1 month after natural infection and up to I year following vaccination. In contrast, IgA to pneumococcal cell wall polysaccharide was both polymeric and monomeric. Moreover, the form of IgA in response to polyribosyl-ribitol-phosphate (PRP), the capsular polysaccharide of Haemophilus influenzae type b, was predominantly monomeric in the sera of 8 of 10 subjects tested 1 to 3 months after vaccination with either PRP alone or the diphtheria toxoid conjugate of PRP. We conclude that systemic responses to pneumococcal capsular polysaccharides are distinct in the production of predominantly polymeric IgA over time. The persistence of polymeric IgA may facilitate binding and clearance of pneumococci from the systemic circulation or reflect limited maturation of the immune response to pneumococcal capsular polysaccharides.     

Immunoglobulin synthesis and gene rearrangement in ataxia-telangiectasia B-lymphoblastoid cell lines

We have analysed the surface immunoglobulins, cell supernatant immunoglobulins and rearrangement of genes specifying these markers in Epstein-Barr virus-transformed lymphoblastoid cell lines, produced from normal individuals and patients with the genetic disorder ataxia-telangiectasia (A-T). Surface IgG and IgM were detected in both normals and A-T patients, while IgA was only present in the controls at a low level. Cell supernatant IgG or IgM was present in controls and some A-T patients, but the majority of A-T patients had both present. No IgA was detected in supernatants from either cell type. All of the cell lines studied showed rearrangement of immunoglobulin heavy chain genes and expression of mRNA. The results described here demonstrate that reduced IgA is not confined to A-T cells and they do not reflect the low levels of serum IgA in A-T patients.     

Spontaneous expression of a low affinity Fc receptor for IgA (Fc alpha R) on human B cell lines

Expression of receptors for IgA (Fc alpha Rs) was investigated on a panel of 35 human B cell lines by labelling with human secretory IgA (0.5 mg/ml) and flow cytometry analysis after staining with fluoresceinated goat anti-human secretory component and/or anti-alpha chain F(ab')2 fragments. Receptors for IgA could be demonstrated on one out of nine Burkitt's lymphoma cell lines, three out of five myeloma cell lines and five out of 21 lymphoblastoid cell lines. The percentage of Fc alpha R-positive cells within the same B cell line varied upon repeated examination. Human dimeric IgA1 lambda myeloma protein revealed the same number of IgA receptor positive cells as did secretory IgA, whereas monomeric IgA did not bind to Fc alpha R. Detection of Fc alpha R was not inhibited when the tests were carried out in the presence of human dimeric IgG, IgM, asialo-orosomucoid, and secretory component but it was abrogated by pre-treatment of the cells with trypsin. The binding characteristics of Fc alpha Rs were studied on the myeloma cell line Esteve, using 125I-labelled human dimeric IgA and secretory IgA. The binding was dose-dependent with rapid kinetics and specific inhibition by unlabelled secretory IgA. Scatchard plot analysis resulted in an equilibrium constant K ranging from 3.2 to 4.7 x 10(6) M/l. No correlation was observed between Fc alpha R expression and differentiation stage, monoclonality, polyclonality of the cell lines, or Ig class produced by the B cells.     

Humoral immune responses in periodontal disease may have mucosal and systemic immune features

The humoral immune response, especially IgG and IgA, is considered to be protective in the pathogenesis of periodontal disease, but the precise mechanisms are still unknown. Immunoglobulins arriving at the periodontal lesion are from both systemic and local tissue sources. In order to understand better the local immunoglobulin production, we examined biopsy tissue from periodontitis lesions for the expression of IgM, IgG, IgA, IgE and in addition the IgG and IgA subclasses and J-chain by in situ hybridization. Tissues examined were superficial inflamed gingiva and the deeper granulation tissue from periodontal sites. These data confirm that IgM, and IgG and IgA subclass proteins and J-chain can be locally produced in the periodontitis tissues. IgG1 mRNA-expressing cells were predominant in the granulation tissues and in the gingiva, constituting approx. 65% of the total IgG-expressing plasma cells. There was a significantly increased proportion of IgA-expressing plasma cells in the gingiva compared with the granulation tissue (P < 0.01). Most of the IgA-expressing plasma cells were IgA1, but a greater proportion expressed IgA2 mRNA and J-chain mRNA in the gingival tissues (30.5% and 7.5%, respectively) than in the periodontal granulation tissues (19% and 0-4%, respectively). The J-chain or dimeric IgA2-expressing plasma cells were located adjacent to the epithelial cells, suggesting that this tissue demonstrates features consistent with a mucosal immune response. Furthermore, we were able to detect the secretory component in gingival and junctional epithelial cells, demonstrating that the periodontal epithelium shares features with mucosal epithelium. In contrast, deeper tissues had more plasma cells that expressed IgM, and less expressing IgA, a response which appears more akin to the systemic immune response. In conclusion, this study suggests that immune mechanisms involved in the pathogenesis of periodontitis may involve features of both the mucosal and systemic immune systems, dependent on tissue location.     

Secretory Immunity in the Female Reproductive Tract

PROBLEM: Antibodies and antibody-producing cells display a different and characteristic distribution in body fluids and tissues. METHOD: We have investigated the tissues of the female reproductive tract to determine whether the distribution of immunoglobulin-producing cells and the contents of cervical secretions were similar to those found in tissues of the secretory immune system. RESULTS: Immunohistochemical examinations of female genital tissues revealed the presence of plasma cells that secrete IgA (and in lower numbers IgM and IgG) especially in the subepithelial layers of the uterine endo- and ectocervix, fallopian tubes, and vagina. Both IgA1- and IgA2-producing plasma cells were found in approximately equal proportions. The presence of J-chain in the IgA-secreting cells suggests the synthesis of polymeric IgA (plgA). Epithelial cells lining the fallopian tube and endocervix were positive for secretory component (SC), which is required for the transepithelial transport of pIgA into external secretions. Cervical mucus was collected and the molecular forms of IgA were separated using column chromatography. Approximately 80% of IgA in cervical mucus was polymeric compared with 55% in the vaginal fluid. CONCLUSIONS: These data indicate that all effector components of the mucosal immune system are present in the female reproductive tract. The immunization routes that lead to a secretory IgA (S-IgA) response need to be further explored.     

Mouse IgA inhibits cell growth by stimulating tumor necrosis factor-alpha production and apoptosis of macrophage cell lines

Potent Fcalpha-mediated actions of IgA have previously been shown for myeloid cells from man, but much less is known in relation to murine cells. Here, we report that mouse monoclonal IgA, irrespective of their antigenic specificity, inhibit the proliferation of mouse macrophage cell lines. The anti-proliferative activity was manifested by both monomeric and polymeric mouse IgA, but not by mouse monoclonal IgG and IgM. Growth of J774 cells was significantly inhibited during the 4-8 days of logarithmic growth, followed by a subsequent recovery of cell numbers prior to the stationary phase. We demonstrated that IgA binds to J774 cells, stimulates tumor necrosis factor (TNF)-alpha production and induces apoptosis which is not dependent on NO or FAS/CD95. We also demonstrated that IgA, in synergy with IFN-gamma, induced TNF-alpha production and apoptosis of thioglycollate-elicited mouse peritoneal macrophages. Thus, the in vitro actions of IgA described may also play a regulatory role for mouse macrophages in vivo.     

Interleukin-4 suppresses immunoglobulin production by peripheral blood lymphocytes of patients with common variable immunodeficiency (CVI) induced by supernatants of T cell clones.

Supernatants of both CD4+ and CD8+ alloreactive T cell clones induced IgM, IgG and IgA synthesis by peripheral blood lymphocytes (PBL) of healthy donors in vitro. These supernatants were also tested on their capacity to induce immunoglobulin production by PBL of four patients with CVI and one patient with CVI and thymoma. A low degree of IgM, IgG and IgA production was induced in one patient with CVI. In the patient with CVI and thymoma, induction of IgG and IgA synthesis was in the normal range, whereas IgM production was reduced. In the three other patients only a low production of IgM was induced. Interestingly, pre-incubation of the PBL for 24 h with interleukin-4 (IL-4) suppressed immunoglobulin production both by PBL of the patients with CVI and healthy donors. The strongest inhibitory effects were observed on IgA synthesis. These data indicate that B cells of three patients with CVI can not be induced to switch to IgG or IgA producing cells in vitro. In contrast, B cells of the patient with CVI and thymoma were able to respond to the relevant B cell growth and differentiation factors present in the T cell clone supernatants, suggesting that the T cells of this patient may fail to produce these factors. However, the proliferative responses of the T cells to phytohaemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM), were normal in all five patients tested. In addition, the interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) production by PBL of the five patients was also in the normal range. Although only a small number of patients was tested, these results support the view that defects in both regulatory T cell functions and/or intrinsic B cell defects may contribute to the pathogenesis of CVI.     

Surface expression of secretory component and HLA class II DR antigen on glandular epithelial cells from human endometrium and two endometrial adenocarcinoma cell lines

The expression of secretory component (SC) by human glandular endometrial cells cultured invitro was significantly increased by estradiol in the medium. Interferon-gamma and interleukin-4 stimulated the expression of SC only in the presence of estrogen. Tumor necrosis factor-alpha plus estrogen also caused a significant increase in the number of cells expressing SC. HLA class II antigen DR was detected on few glandular epithelial cells of human endometrium cultured in control medium, whereas interferon-gamma and interleukin-4, but not tumor necrosis factor-alpha, caused significant increases in the expression of DR. Estrogen in the culture medium did not significantly affect DR expression. The human endometrial adenocarcinoma cell lines, HEC and RL-95, expressed SC in approximately 50 and 20% of the cells. Also, approximately 20% of the RL-95 cells stained for DR antigen. Interferon-gamma did not influence the degree of expression of either surface marker of the two cell lines. Cells of both lines bound polymeric IgA and IgM but showed little to no binding of monomeric IgA, IgG, or an IgM previously shown not to bind SC.     

In vitro response of human peripheral blood lymphocytes of protein A. DNA synthesis and generation of cells synthesizing the three major classes of Ig.

Increased DNA synthesis and immunoglobulin secretion was observed in human peripheral blood lymphocytes (PBL) cultured in vitro with soluble protein A from Staphylococcus aureus (Sp-A). Optimal Ig secretion was obtained in 6 day cultures containing 1 x 10(6) cells/ml and 10 microgram/ml Sp-A. The presence of 5 x 10(-5) M 2-mercaptoethanol in the culture medium as well as careful selection of foetal calf serum were needed for optimal results. In response to Sp-A stimulation, the three main classes of immunoglobulins were secreted by PBL. In some individuals, concentration of Sp-A optimal for IgG and IgM secretion inhibited IgA production. Immunoglobulin-containing cells were less abundant (0.5--5% of total cells) and smaller in Sp-A than in PWM-stimulated cultures (5--15%). The data suggest that Sp-A and PWM stimulated different subsets of circulating lymphocytes.     

IgA specific helper factor (alpha HF) in human colostrum.

Induction of immunoglobulin secretion by human colostrum was investigated using human peripheral blood lymphocytes (PBL) and Epstein-Barr virus transformed human B lymphoblastoid cells. Stimulation of the cells with colostrum induced IgA plaque forming cells but neither IgG nor IgM plaque forming cells, indicating the occurrence of IgA specific helper factor (alpha HF) in human colostrum. alpha HF activity was eluted into fractions with an apparent molecular weight of about 80 kD by gel filtration, and with a PI range of 5.8 to 6.2 by chromatofocusing. IgA secreted by PBL stimulated with alpha HF had a similar molecular weight distribution to that of IgA in human colostrum. From these results a hypothesis is proposed; IgA-committed B cells in the mammary gland differentiate to plasma cells producing dimeric IgA after stimulation by alpha HF so that the dominant immunoglobulin in human colostrum is IgA.