The secretory IgA system of the gut

Most commonly, humoral immunity manifested in the gastrointestinal tract of mammals is due to the presence of secretory IgA antibodies. Antibody specificities have been detected in the secretory IgA of gut secretions to a wide range of naturally occurring viral and bacterial components and to test antigens such as chemically modified proteins. Much of the IgA found in gut secretions is synthesized and secreted locally by the abundant plasma cells of the lamina propria. Development of methods for establishing local protective immunity in the gut requires knowledge of the origins of these plasma cells and of the whereabouts of their precursors when they are susceptible to antigen-driven proliferation and/or maturation. The Peyer's patches have been shown to contain a population of B lymphocytes especially rich in precursors for IgA plasma cells and in cells which can repopulate gut lamina propria with such IgA plasma cells. The Peyer's patches also appear to 'sample' gut antigens, in that small amounts of antigens are passed intact through their dome epithelial cells. Recent experiments bearing on the origins, differentiation and maturation, antigen sensitivity, migration and lodging of precursors for gut IgA plasma cells are discussed. We use the following three systems: (1) congenic transfer of cells from different murine lymphoid cell sources or mixtures of these (CB20 leads to BALB/c or BALB/c leads to CB20) and the use of allo-antisera to IgA allotypic determinants to assess their potential to impart an adoptive IgA antibody response to the recipient and to repopulate its histocompatible lamina propria with IgA plasma cells; (2) clonal precursor analysis (the method of Klinman) both to enumerate antigen-sensitive cells in different tissues of mice and to evaluate their potential to generate plasma cells making particular isotypes and idiotypes of antibodies; (3) use of pairs of Thiry-Vella loops in rabbits, each member either bearing or lacking a Peyer's patch, and quantitation of antibodies of each isotype and of total secretory IgA to assess the response of each loop with the time after local immunization. The results from all three systems provide strong evidence for the importance of Peyer's patches in supplying cells responsible for local humoral immunity and suggest both a differentiative pathway for IgA precursors and their whereabouts when antigen may cause the expansion of a population of specific cells.

Structure of the heavy chain from strain 13 guinea pig immunoglobulin G1: isolation of cyanogen bromide fragments

Guinea pig serum contains two isotypes of immunoglobulin G: IgG1 and IgG2. These immunoglobulins are antigentically distinct from each other and they mediate different biologic processes in the same guinea pig, although they share the ability to bind the same antigen. An attempt was made to study the primary structure of the gamma1 heavy chain from IgG1 in comparison with the largely known primary structure of the gamma-heavy chain from IgG2, with the aim of demarcating the structural differences between these molecules. IgG1 was isolated from the serum of immune strain 13 guinea pigs. Both IgG1 and the gamma1 chain were digested with CNBr. Nine fragments were isolated from both digests by gel filtration procedures before and after reductive cleavage of disulfide bonds. These fragments appear to account for the entire approximately 444 residues in the gamma1 chain. Amino acid composition data of CNBr fragments suggest that at least the amino terminal approximately 182 residues of the gamma1 and gamma2 chains are very similar. Two of the fragments which have been isolated have amino acid compositions suggesting their derivation from the "hinge" region and carboxyl terminus of the gamma1 chain.

Structural and thermodynamic basis of affinity in anti-dinitrophenyl antibody

The thermodynamic quantities of the anti-dinitrophenyl antibody-hapten interaction are reported for rabbit, goat, and guinea pig antibodies. Rabbit and goat antibodies had similar exothermic enthalpy changes for their reaction with 2,4-dinitrophenyl-L-lysine (-13.9 and -14.8 kcal/mol, respectively). The enthalpy change with guinea pig antibody was much less exothermic (-8.7 kcal/mol), and this value was the same for two guinea pig antibody preparations that differed in affinity by almost two orders of magnitude. A heterogeneous goat anti-dinitrophenyl antibody preparation was fractionated on a molecular sieve column in the presence of a bivalent ligand, a procedure that has been reported to separate antibodies according to differences in the depth of interaction with the ligand. The relationship of these differences in apparent site depth to changes in interactions with the hapten tail was examined by comparing the affinities of various fractions for two haptens. The results show that the presumed deeper sites have stronger interactions with the hapten tail. These studies suggest that the heterogeneity of anti-dinitrophenyl antibodies with respect to affinity results from differences in entropy driven lysyl side-chain interactions which arise from a heterogeneity in antigen binding site depth.

Anti-dinitrophenyl antibody production in strain 13 guinea pigs fed or sensitized with dinitrochlorobenzene

Guinea pigs fed dinitrochlorobenzene (DNCB) in corn oil become unresponsive tosensitization by later percutaneous applications of DNCB in olive oil. Sera taken from animals after feeding DNCB or after feeding and intradermal stimulation with DNCB contained no antibody detectable with 2,4-dinitrophenyl (DNP)-labeled T4 bacteriophage; if any antibody was present, its concentration was below 2 mu g/ml. Guinea pigs fed DNCB and then immunized with DNP on a foreign carrier, keyhole limpet hemocyanin (KLH), produced as much antibody 16 to 18 days later as did animals which had only been sensitized by intradermal injection of DNCB in phosphate-buffered saline and then immunized with DNP-KLH. The amount of antibody produced to DNP-KLH WAS MEASURED AT INTERVALS. In the fed animals, the titer either remained approximately the same or increased with time. In contrast, the sera of sensitized guinea pigs contained a decreasing antibody titer when the first and last bleedings were compared. Isoelectric focusing was carried out with sera from DNP-KLH-immunized animals after the sera were first mixed with a radiolabeled hapten. The antibody-hapten profiles revealed that the DNCB-fed animalss contained predominatly IgG2 in their serum by the time of their initial bleedings, whereas sensitized animals still contained a considerable proportion of more acidic antibodies having marked charge heterogeneity. Equilibrium dialysis measurements onpurified antibody from fed animals indicated an average binding affinity for hapten equivalent to that of purified antibody from sensitized animals. Feeding of DNCB did not cause any obvious decrease in the number of lymphoid cells able to bind 125I-labeled guinea pig IgG. Lack of reduction of the average binding affinity coupled with the retention of antigen-binding lymphoid cells, permit the conclusion that feeding DNCB to guinea pigs under the conditions used did not induce an unresponsiveness or a deletion of those cells which have the potential to produce anti-DNP antibody. Thus, feeding of guinea pigs with DNCB in oil seems to induce a central tolerance at the T cell level with adversely affecting their B lymphocytes. The antibody response obtained by immunization with DNP conjugated to a foreign carrier is not only quantitatively equivalent to that obtained in control animals but qualitatively it appeared to be more mature with respect to charge at a relatively early time (16 to 18 days. Since the antibody levels in serum from fed animals increased or remained approximately constant with time instead of waning as occurred in the DNCB-sensitized animals, feeding or sensitization with DNCB may also have affected some cell or cell product important in the regulation of antibody production.

Rabbit Peyer's patches, appendix, and popliteal lymph node B lymphocytes: a comparative analysis of their membrane immunoglobulin components and plasma cell precursor potential

We have characterized and compared the differentiative potential of B lymphocytes obtained from rabbit appendix (APP), Peyer's patches (PP), and popliteal lymph nodes (PLN) by immunofluorescence analysis of membrane immunoglobulin (Ig) components, by radioiodination of membrane components followed by isolation and identification of cell surface Ig, and by cell transfer studies. As assessed by cell transfer lymphoid cells from PP and APP appear to be highly enriched sources of IgA plasma cell precursors. In addition, these populations of lymphocytes have a small but significant potential to give rise to IgM and IgG plasma cells. In contrast, as shown previously (1), lymphocytes from PLN have a comparatively small potential to generate IgA plasma cells. The ability of cells from PLN and PP to give rise to plasma cells is correlated with the presence of 35 to 38% of lymphocytes from both sources having membrane light chain determinants detectable by immunofluorescent staining. When the cells were stained directly for mu chain determinants, about 33% of PLN cells and 28% of PP cells were positive. These latter percentages were shown to reflect cells bearing both endogenously synthesized b4 light chain and mu heavy chain. By indirect immunofluorescence, alpha and gamma chain determinants were also detected on PP and PLN cells; however, these Ig did not appear to be products of the cells which bore them as they were not regenerated after removal of Pronase. It was further demonstrated that purified rabbit copro-sIgA and colostral sIgA are cytophilic for PP and PLN cells. The results are discussed with respect to the origin of IgA plasma cells and the postulated bursal role of mammalian gut-associated lymphoid tissue.

Specificity of antibodies: primary structural basis of hapten binding

The primiary structure of the 83 residues of the NH(2)-terminus of the V(II), region was determined for each of three different antibodies to hapten which were produced in inbred guinea pigs. Each antibody had a different and distinctive primary structure within each of the two "hypervariable" regions (Hv1 and Hv2) included in the analyzed part of the variable region of the heavy chain. The sequences of Hvl and Hv2 in the three antibodies were either unique or of restricted variability compared with those of "normnal" immunoglobulin G2. Further implication of Hv1 and Hv2 in contributing to ligand-binding specificity of antibodies came from the placement of residues modified by affinity labeling reagents in these hypervariable regions.

Restriction of gene expression in B lymphocytes and their progeny. III. Endogenous IgA and IgM on the membranes of different plasma cell precursors

Fluorescent antibody staining with antibodies to the f and g locus allotype markers present on rabbit alpha-chains revealed that the alpha-chain is the heavy chain on the Peyer's patch lymphocytes which previously had been shown to be the precursors of IgA-producing plasma cells. In addition, lymphocytes which had been stripped of membrane Ig with pronase and then cultured overnight to allow the sole expression of endogenous membrane Ig were found to have either the micro-chain or the alpha-chain on their membranes, but not both. These results suggest that most lymphocytes are restricted to the synthesis of one class of heavy chains at a time and that the commitment to synthesizing that particular heavy chain is maintained during the differentiation of lymphocytes into plasma cells. The proportion of lymphocytes with membrane alpha-chains is higher in the Peyer's patch and appendix, two gut-associated lymphoid tissues (GALT), than in other lymphoid tissues. Since the GALT are enriched sources of precursors for IgA-producing plasma cells compared to nongut-associated tissues, the presence of cells bearing membrane alpha-chains correlates well with the relative abilities of these tissues to generate IgA plasma cells.

Restriction of gene expression in B lymphocytes and their progeny. II. Commitment to immunoglobulin heavy chain isotype

To determine whether or not B lymphocytes are committed to the synthesis of a single immunoglobulin heavy chain isotype during their differentiation into plasma cells, rabbit lymph node and Peyer's patch cells were separated into populations with and without membrane IgM, using a fluorescence-activated cell sorter (FACS). The potential of the micro-bearing (micro+) and non-micro-bearing (micro-) cells to give rise to plasma cells both in vivo after transfer into irradiated recipients and in vitro in the presence of pokeweed mitogen was assessed by immunofluorescence techniques, and the relative proportions of the cytoplasmic Ig-stained cells (CSC) synthesizing each class of heavy chains were determined. Most of the CSC arising in vitro from micro-bearing lymph node and Peyer's patch cells contained IgM; all IgM CSC appeared to be derived from micro+ cells. Peyer's patch lymphocytes, however, did not generate IgM CSC after cell transfer and thus may be functionally different from lymph node micro+ cells. It was found also that nearly all of the many IgA CSC generated by Peyer's patch lymphocytes either in culture or after transfer were derived from micro- cells. Further fractionation of these micro- cells with the FACS after they had been membrane stained with anti-b locus allotype reagents revealed that the precursors of IgA CSC belong to a minor population of cells which do have b locus light chain determinants on their membranes, although they do not have detectable micro-chains. These cells are not found in lymph nodes. Although the majority of Peyer's patch and lymph node cells were found to be precommitted to the synthesis of a single heavy chain isotype, a small proportion of cells may not be similarly restricted. Some of the CSC with membrane IgM were found to contain cytoplasmic IgA or IgG. In addition, micro+ populations did give rise to low numbers of IgA and IgG CSC. The implications of these results, obtained under experimental conditions, on the normal differentiation of B lymphocytes in situ are discussed.

Restriction of gene expression in B lymphocytes and their progeny. I. Commitment to immunoglobulin allotype

Lymphocytes from b(5)/b(9) rabbits were stained in suspension with fluorescent antiallotype antibody reagents to selectively label with fluorescent molecules those cells bearing membrane immunoglobulin (Ig) of the b5 or b9 allotype. After staining, the cells were separated by the fluorescence-activated cell sorter into populations markedly enriched in cells bearing b5 or b9 membrane Ig or totally depleted of cells with detectable membrane Ig. The potential of these separated cells to give rise to Ig-synthesizing plasma cells either in vivo after transfer into irradiated recipients or in vitro during culture in the presence of phytohemagglutinin or pokeweed mitogen was assessed by immunofluorescence. The relative proportion of b5 and b9 cytoplasmic Ig-stained cells (CSC) arising from the separated cells was determined to test directly whether B lymphocytes and their progeny are committed to the synthesis of Ig of one allotype. It was found that b5- and b9-bearing cells gave rise almost exclusively to b5- and b9-producing plasma cells, respectively, in both the in vivo and in vitro assay systems. Most of these CSC were probably not derived from previously existing CSC but arose as the result of the differentiation of lymphocytes with membrane Ig. When cell populations totally depleted of Ig-bearing lymphocytes were cultured, very few CSC were found, indicating that the majority of immediate precursors of CSC have membrane Ig. These results suggest that individual B cell clones are phenotypically restricted to the expression of immunoglobulin genes on one chromosome; the significance of this clonal allelic exclusion is discussed.

Peyer's patches: an enriched source of precursors for IgA-producing immunocytes in the rabbit

The proliferative and differentiative potential of Peyer's patch, peripheral blood, and popliteal lymph node cells was assessed by allogeneic cell transfer followed by quantitation of donor immunocytes by immunofluorescence. It was found that Peyer's patches are a highly enriched source of cells which have the potential to proliferate and differentiate into IgA-producing immunocytes and that the Peyer's patch cells are far more efficient in seeding the gut of irradiated recipient rabbits with donor cells that give rise to immunoglobulin-producing cells than cells from peripheral blood or popliteal lymph nodes.

Selective simulation of allelic expression: effectf antibodies to allotypic markers on lymphoid cells

Peripheral blood leukocytes from rabbits which were heterozygous (b(5)/b(9)) for markers on their immunoglobulin light chains were maintained in vitro for up to 24 hours in the presence or absence of antibody to b9. After culture they were transferred into lethally irradiated b(4)/b(4)hosts. Recipients of cells exposed to antibodies to allotype markers showed a striking increase in concentration of circulating b9 molecules and number of b9 plasma cells in their spleens compared pared to control animals receiving untreated cells from the same donor. There was no appreciable difyerence between the two groups of recipients with respect to their content of b5 molecules and immunocytes.

Immunoglobulins and immunocytes

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The partial sequence of two large peptides from the N-terminal half of heavy chains from normal rabbit immunoglobulin G

The partial amino acid sequence of two large peptides is described. These were prepared from the N-terminal half of the heavy chain of immunoglobulin G from pooled normal rabbit serum by tryptic digestion after the in-amino groups of the lysine residues had been blocked with S-ethyl trifluorothioacetate. These peptides are believed to account for about 145 residues of fragment C-1, the N-terminal section of rabbit immunoglobulin G heavy chain prepared by cyanogen bromide cleavage. The evidence from the present paper and the preceding paper (Cebra, Givol & Porter, 1968) suggests that it may be possible to deduce a predominant amino acid sequence for most, if not all, of this section of the molecule.

Common peptides from the N-terminal half of heavy chain of immunoglobulin G from normal rabbit serum and a specific antibody

Fragment C-1, the N-terminal half of the heavy chain of rabbit immunoglobulin G, was prepared by cyanogen bromide cleavage from the heavy chain of immunoglobulin G obtained both from the pooled serum of normal rabbits and from specific anti-dinitrophenyl antibody. Tryptic digestion of fragment C-1 after the lysine residues had been allowed to react with S-ethyl trifluorothioacetate led to the isolation of six peptides from inert immunoglobulin G and specific antibody that appear to account for most of this section of the heavy chain. This approach should make possible comparative sequence studies of the Fd section of the heavy chain from different allotypes and from specific antibodies.

Identical allotypic markers of heavy polypeptide chains present in different immunoglobulin classes

Purified IgA molecules, prepared from rabbit colostrum, have the same allotypic markers of the heavy (H) polypeptide chain as are present in the serum IgG of the same individual. When the dimeric molecule of rabbit colostral IgA is dissociated into its sub-units by reduction, its capacity to absorb an appropriate anti-allotypic antibody is quantitatively identical with that of the serum IgG of the same animal. It is concluded that there are neither qualitative nor quantitative differences in the antigenic expression of the allotypic determinants of the a locus present on the rabbit γ and α chains.

The relative proportions of IgG-, IgAand IgM-containing cells in rabbit tissues during experimental trichinosis

The relative proportions of IgG, IgM and IgA immunoglobulin-containing cells were determined in the intestinal mucosa, spleen, popliteal lymph nodes and diaphragm of rabbits after a single infection and after hyperinfection with Trichinella spiralis. Staining with pairs of immunofluorescent reagents, specifically reactive with γ, μ or α immunoglobulin heavy chains and labelled with contrasting fluorochromes, permitted direct counting of cells containing two different immunoglobulin classes in a single tissue section. By employing two different pairs of reagents on adjacent sections the relative numbers of cells containing IgG, IgM and IgA were calculated.

The observed cellular distribution of γ, μ and α heavy chains in the rabbit intestinal mucosa corresponded with the reported distribution in the human intestine. A relative increase in IgM-containing cells in the mucosa was observed after early infection with Trichinella, followed by an apparent increase in cells with IgG late in infection and after hyperinfection. The proportion of cells staining for IgA remained uniformly high in the intestine throughout the course of infection.

The proportions of cells containing different immunoglobulin classes in the spleen contrasted with those observed in the intestinal mucosa, particularly with respect to cells containing α chain. IgA cells made up 2–10 per cent of the immunoglobulin-containing cells in the spleen as compared to 80–90 per cent in the intestinal mucosa. Most spleen sections showed an increase in IgM cells late in infection with Trichinella and after hyperinfection. The proportions of immunoglobulin-containing cells in the popliteal lymph nodes generally paralleled those observed in the spleen.

Local cellular infiltration of the diaphragm occurred at the time of larval encystment. Immunoglobulin-containing cells were often prominent and the cellular distribution of immunoglobulin classes resembled that found in the spleen.

The indirect fluorescent antibody technique was employed to detect anti-Trichinella antibody of the three immunoglobulin classes in sera and extracts of the gut of hyperinfected rabbits. Only IgG antibody was detected in gut extracts although both IgG and IgA were demonstrated to be present by Ouchterlony analysis. Both IgG and IgA were demonstrated to be present by Ouchterlony analysis. Both IgG and IgM antibodies were demonstrated in the sera.

Rabbit lymphoid cells differentiated with respect to alpha-, gamma-, and mu- heavy polypeptide chains and to allotypic markers Aa1 and Aa2

Lymphoid cells present in spleen and lymph nodes of hyperimmune rabbits were found to be differentiated with respect to the class of immunoglobulin heavy chain which they contained. The relative proportions of cells containing the various heavy chains were as follows: alpha-chain (5 to 8%), micro-chain (14 to 21%), and gamma-chain (71 to 81%). The allotypic markers Aa1 and Aa2, found on heavy chains, were also found to be separately localized in cells of Aa(1)/Aa(2) heterozygous rabbits. The ratio of cells in spleen and lymph nodes containing the Aa1 marker to those containing the Aa2 marker varied with individual rabbits; the range was 53 to 88% Aa1 versus 12 to 47% Aa2.