Population dynamics of natural antibodies in normal and autoimmune individuals

We have measured the quantities of naturally occurring autoantibodies in the serum of normal, unmanipulated individuals. These changes over time following broad-band complex dynamical patterns that are similar in mouse and man. The patterns more likely reflect the network architecture of the natural antibody repertoire, regulating the activation and decay of individual clones. The temporal changes of both disease-specific and nonspecific autoantibodies are consistently modified in autoimmune individuals.

Normal serum immunoglobulins participate in the selection of peripheral B-cell repertoires

In B-cell development, expression of immunoglobulin heavy-chain variable-region (VH) gene repertoires is determined by genetic mechanisms that favor rearrangement of the most D-proximal genes, resulting in overutilization of the VH7183 gene family early in ontogeny and in differentiating B cells of the adult bone marrow. Maturation of the immune system is accompanied by a decreased expression of VH7183 genes in the peripheral immunocompetent B-cell pool of adult animals. By comparing VH gene family expression in the bone marrow (emergent) and peripheral (available and actual) B-cell repertoires of germ-free and conventionally raised BALB/c mice, we found that peripheral selection of VH gene family utilization does not occur in germ-free animals. Reconstitution of germ-free mice with normal serum immunoglobulins purified from syngeneic donors reestablishes selection of VH7183-expressing B cells. Our results indicate that preimmune B-cell repertoires are selected in normal animals by environmental antigens and serum immunoglobulins.

Xid immunodeficiency imparts increased parasite clearance and resistance to pathology in experimental Chagas' disease

Infection of several mouse strains with Trypanosoma cruzi stimulates high levels of T and B lymphocyte activities which persist during the chronic phase and is followed by specific immunosuppression and severe autoimmune pathology. Infected BALB.Xid mice carrying an X-linked mutation and lacking CD5 B cells, display poor B cell responses to T. cruzi infection, accompanied by low levels of specific and non-specific immunoglobulins in the serum. However, these animals control parasitemia, do not show the wasting observed in BALB/c mice, and develop almost no pathology early in the chronic phase. The infection of (BALB.Xid female x BALB/c male) F1 animals shows that immunodefective males behave like Xid animals in contrast to females which respond as normal BALB/c mice. These results indicate that the Xid locus controls lymphocyte responses, parasite clearance and pathology in experimental Chagas' disease.

Normal serum immunoglobulins influence the numbers of bone marrow pre-B and B cells

The homeostatic mechanisms controlling B lymphocyte output from bone marrow are not well understood. The present experiments evaluated putative influences of circulating immunoglobulins (Ig) on bone marrow (BM) pre-B and B cell populations. Injections into normal mice of Ig isolated from normal mouse serum, resulted in a dose-dependent and reversible reduction in numbers of BM B lineage cells, in particular of small B220+ surface IgM- cells. Maximal effects were observed upon injection of isologous polyclonal Ig and were independent of mature T cells. These results suggest a feedback modulation of peripheral Ig on cellular activities in BM B lineage compartments, mediated by mechanisms that seem to involve the variable regions of the Ig molecule.

Second generation immune networks

Network approaches have had little impact on immunology because they have addressed the wrong questions. They have concentrated on the regulation of clonal immune responses rather than on the supraclonal properties of the immune system that emerge from its network organization, such as natural tolerance and memory. Theoretical advances, observations in unimmunized mice and humans, and the success of novel therapeutics in autoimmune diseases have recently promoted a new burst of research on the structure, temporal dynamics and metadynamical plasticity of immune networks.

Stimulation of B and T cells by in vivo high dose immunoglobulin administration in normal mice

Adult BALB/c mice were injected intravenously with a preparation of pooled normal murine IgG (400 mg/kg/day, on five consecutive days) and studied 8, 15, and 60 days later. High dose IgG administration increased the total numbers of splenic activated B and CD4+ (but not CD8+) T cells, as well as the numbers of splenic Ig-secreting cells, particularly in the IgG isotypes. Reactivities to some autoantigens, but not to bacterial or other heteroantigens, were selectively amplified amongst IgM-secreting cells. IgG administration did not alter the specific primary immune response to heterologous erythrocytes or bacterial dextran. No cellular alterations were detected in the lymph nodes or peritoneal cavity of treated animals. Most of these effects subsided with time, but some autoantibody reactivities remained elevated 60 days later. The present results suggest that the therapeutic effects of high dose IgG administration which have been reported in human diseases might be associated with the immunostimulatory activities of such treatment.

Role of B and T lymphocytes in the specific immunosuppression induced by a protein released by porcine monocytes infected with African swine fever virus

Some immunobiological aspects of host responses to an immunosuppressive protein (p36) released by porcine monocytes upon infection with African swine fever virus were analysed in a murine system. Treatment of normal, adult C57BL/6 mice with p36 (i) significantly delayed allogenic skin graft rejection; (ii) suppressed the specific plaque-forming cell response to immunization with heterologous erythrocytes; but (iii) induced marked increases in the numbers of 'background' splenic Ig-secreting plaque-forming cells. Cytofluorometric analysis of spleen cells revealed that a considerable fraction of all B cells, as well as CD4 and CD8 T lymphocytes, undergo blast transformation after p36 treatment. The immunosuppressive effects do not seem to result from 'antigenic competition', for they cannot be induced by even higher doses of pig albumin or by culture products of non-infected pig monocytes. Suppression of specific antibody responses and stimulation of 'background' plaque-forming cells are both T cell-dependent, since they are markedly reduced in thymectomized mice and in animals treated with anti-CD4 or anti-CD8 antibodies. This suggests the relationship between non-specific stimulation and specific suppression of 'unrelated' immune responses and reinforces the notion that viral-associated immunosuppression may be due to overstimulation. The present murine experimental model may prove valuable in the study of immunosuppression associated with infection, even for microorganisms which do not infect mice.

Endogenous VH gene family expression in immunoglobulin-transgenic mice: evidence for selection of antibody repertoires

VH gene family expression in single cells of the emergent, available and actual B cell repertoires of C57BL/6 mice was compared to that of two immunoglobulin (Ig)-transgenic B6 lines (B6-Sp6 and M54). We found that less than 5% of bone marrow cells of transgenic mice express endogenous VH genes and that the vast majority (95%) of the peripheral, mature B cell repertoire in these animals is composed of cells expressing the VHJ558 transgenic family. Unimmunized transgenic mice, however, diversify VH gene family usage by 'background' Ig-secreting cells in the spleen, greater than 50% of which express endogenous VH genes. The pattern of endogenous VH gene family expression in the actual repertoire of B6-Sp6 mice is indistinguishable from that of normal B6 mice. In contrast, actual repertoires of M54 mice differ by a 4- to 5-fold higher representation of the VHQ52 family. These results demonstrate a powerful positive selection of B cells into the secretory compartments of unimmunized animals, show that actual and available repertoires differ very markedly, and suggest that V region interactions participate in the selection of 'natural antibody' repertoires.

V beta 17 gene polymorphism in wild-derived mouse strains: two amino acid substitutions in the V beta 17 region greatly alter T cell receptor specificity

Of 41 wild-derived mouse strains analyzed, 14 contained T cells bearing V beta 17 receptors in spite of the concomitant expression of I-E antigens. Reciprocal F1 and F2 hybrids of one of these strains, PWK, with laboratory strains revealed different patterns of V beta 17 T cell deletions from those observed with V beta 17 T cells from SJL, implying that the two V beta 17 regions are associated with recognition of distinct superantigens. The structures of the V beta 17 alleles differ by two amino acid substitutions, which lie together in an area distant from the predicted site of T cell receptor interaction with peptide-MHC complexes but overlapping with that implicated in V beta 8.2 recognition of Mls-1 superantigen. This demonstrates that the self-superantigen leading to V beta 17 T cell deletion varies with the allele of the receptor gene and confirms that T cell deletions by such ligands involve interactions with a region of the V beta domain that is distinct from the conventional combining site.

Inside the thymus, Mls antigen is exclusively presented by B lymphocytes

The ability to stimulate an Mls-1 mixed lymphocyte reaction (MLR) is predominantly expressed by low density B lymphocytes in the spleen and peritoneal cavity of normal adult mice, and is absent in splenic B cells 1 month after lethal irradiation and reconstitution from autologous bone marrow. Coreconstitution of these mice with normal syngeneic peritoneal cells restores the stimulatory potential of splenic B cells, but sorted CD5+ or CD5- IgM+ lymphocytes from peritoneum are equally good stimulators, suggesting that functional Mls-1 expression may require long life spans and selection. Bone-marrow-reconstituted DBA/2 mice that fail to express Mls-1 antigens in the periphery nevertheless maintain T-cell receptor V beta 6 and 8.1 deletions among the newly formed T cells. These findings led us to directly investigate the Mls stimulatory ability of purified antigen-presenting cell populations inside the thymus. We report here that thymic B lymphocytes seem to represent the only intrathymic cell population able to stimulate Mls-1 MLR.

Selection of anti-F protein B-cell repertoires in normal mice

The hypothesis that self-tolerance to F protein antigen exclusively concerns T cells was tested by determining the frequencies of B lymphocytes producing anti-F antibodies in bone marrow (BM), spleen and peritoneal exudate (PEC) cells from normal, immune or tolerant animals, and in responder and non-responder mouse strains. Using an ELISA spot assay and lipopolysaccharide stimulation, we found that anti-F frequencies were highest in BM and "naturally activated" large spleen cells, followed by resting spleen and PEC cells. Anti-F specificities were also induced among "natural" Ig-secreting cells of normal individuals. Specific immunization of responder mice doubled the splenic frequencies, while tolerization had no effect. Similar results were obtained in BALB/c and A/J mice, while C57BL/6 contained fewer anti-F B cells in spleen, but not in BM. These results support the notion that self-tolerance to F antigen can primarily be ascribed to T cells, but they also show F-antigen-specific selection of B-cell repertoires.

Divergency in the specificity of the induction and maintenance of neonatal suppression

Neonatal treatment of BALB/c mice with anti-VHT15 antibodies suppresses serum expression of VHT15 immunoglobulins in adult animals (2 months) which remains for over 8 months in half of the cases. Suppressed mice, however, contain control numbers of B cells expressing genes of the S107VH family and producing VHT15 after mitogenic stimulation. Furthermore, immunization with phosphorylcholine (PC) breaks suppression and stimulates the production of VHT15 anti-PC antibodies. These animals, however, contain no detectable B lymphocytes expressing the T15 idiotype and produce no T15 idiotype-positive antibodies in response to PC. These results are discussed in the context of lymphocyte repertoire selection.

Localization of gamma/delta T cells to the intestinal epithelium is independent of normal microbial colonization

Using monoclonal antibodies identifying all gamma/delta and alpha/beta T cell receptors in cytofluorometric analysis, we have compared the composition of intestinal intraepithelial lymphocytes (i-IEL) in euthymic and athymic germ-free (GF) and conventional (SPF) mice. The results show a marked influence of microbial colonization in the numbers of single-positive (CD4+ or CD8+) alpha/beta i-IEL, but little effect in the pool size or characteristics of gamma/delta i-IEL. In young athymic mice, virtually no alpha/beta i-IEL are detected, while considerable numbers of gamma/delta i-IEL remain, though reduced in GF animals.

Selective peripheral expansion and activation of B cells expressing endogenous immunoglobulin in mu-transgenic mice

Two different lines of C57BL/6 mice (IgHb) carrying complete rearranged mu chain genes from BALB/c (IgMa) were analyzed for the expression and secretion of endogenous as well as transgenic immunoglobulins at the level of single cells. Quantitation of B cells expressing endogenous IgMb by cytofluorometry, limiting dilution analyses of clonal precursors and secretory cell assays revealed a marked selective expansion, activation and terminal differentiation of those cells producing endogenous immunoglobulins. Thus, the very infrequent IgMb-bearing B cells produced in bone marrow of transgenic mice accumulate in spleen, where they are activated and account for roughly half of all natural immunoglobulin-secreting cells. These observations indicate that mu-transgenic mice are valuable in studies of the antibody repertoire selection operating in unprimed animals but their use could be misleading in the analyzing "monoclonal" immune system.

Dibucaine interaction with phospholipid vesicles. A resonance energy-transfer study

Resonance energy transfer between a local anaesthetic, dibucaine (donor) and a set of functionalized probes [n-(9-anthroyloxy)stearic acids, n = 2, 3, 6, 7, 9 and 12 and 16-(9-anthroyloxy)palmitic acid] (acceptors) was found to be an efficient process with a critical radius of transfer Ro = 2.1 nm, this interaction being used to locate the drug in a model membrane system, small unilamellar vesicles of dipalmitoylglycerophosphocholine, both above and below the temperature of the gel-to-the-liquid-crystal transition of the phospholipid. From the sequence of relative quenching efficiencies of dibucaine fluorescence upon incorporation of the probes, it was concluded that the drug intercalates in the membrane near the glycerol backbone of the lipid. In addition, it was found that dibucaine location is not significantly affected upon crossing the phase-transition temperature of the phospholipid. Dibucaine photophysics was also studied and the short lifetime of the neutral form of the anaesthetic with respect to that of the monoprotonated species was attributed to an intramolecular charge-transfer interaction. From the study of its partition coefficient between the membrane and the aqueous phase, it was concluded that the only significant species present in the membrane is the charged one.

Thymic epithelium tolerizes for histocompatibility antigens

The role of thymic epithelium in the establishment of tissue tolerance was analyzed with a murine chimeric system. All T cells differentiated from birth onward in a thymus comprising allogeneic epithelium and syngeneic hematopoietic cells. Embryonic thymic rudiments that contained no hematopoietic cells from C3H (H-2k) donors were grafted to newborn athymic (nude) BALB/c (H-2d) mice. Chimeras that had normal T cell numbers and function rejected third-party skin grafts, but permanently accepted grafts syngeneic to the thymic epithelium. In vitro functional assays did not always correlate with the state of tolerance in vivo. Thus, pure thymic epithelium induces tolerance to histocompatibility antigens.

Thymic epithelium tolerizes for histocompatibility antigens

The role of thymic epithelium in the establishment of tissue tolerance was analyzed with a murine chimeric system. All T cells differentiated from birth onward in a thymus comprising allogeneic epithelium and syngeneic hematopoietic cells. Embryonic thymic rudiments that contained no hematopoietic cells from C3H (H-2k) donors were grafted to newborn athymic (nude) BALB/c (H-2d) mice. Chimeras that had normal T cell numbers and function rejected third-party skin grafts, but permanently accepted grafts syngeneic to the thymic epithelium. In vitro functional assays did not always correlate with the state of tolerance in vivo. Thus, pure thymic epithelium induces tolerance to histocompatibility antigens.

Positive selection of gamma delta T cells

The issue of T-cell repertoire selection has been addressed recently by several laboratories. While evidence has been provided for both negative and positive selection of CD4+ and CD8+ alpha beta T cells, the molecular basis of positive selection remains unclear. In this article Juan Lafaille and colleagues describe molecular features of gamma delta T-cell selection in the fetal thymus. These features were deduced from extensive junctional sequence data of gamma delta T-cell receptor genes in fetal thymocytes. Their data suggest the active participation of a self peptide in the positive selection of gamma delta T cells.

Cellular basis for the age-associated increase in autoimmune reactions

The mechanisms that lead to the increased expression of autoantibodies with age are poorly understood. We have studied the number, size, and density of spleen and peritoneal cells from young and old BALB/c and C57BL/6 mice as well as the frequency of clonal precursors for antibodies to mouse erythrocytes, thyroglobulin, and IgG in these lymphoid preparations. Old mice have a 6-fold increase in the number of resident peritoneal cells and a 2-fold increase in the absolute number of Ly1-bearing B cells in this population. Furthermore, old mice have twice as many large, low density splenic B cells as young mice. The frequencies of B cell clonal precursors for anti-BrMRBC and anti-thyroglobulin antibody-forming cells in old mice were 3-10 times greater than in young mice. In the same cultures, however, no increase in the frequencies of B cell clonal precursors for anti-IgG or anti-DNA antibody forming cells was detected in old compared to young mice. These findings and other data suggest that there are at least two families of B cell autoantibody precursors, one including anti-BrMRBC and anti-thyroglobulin autoantibodies, the other including anti-IgG and anti-DNA antibodies. Studies of the differential regulation of these two families of autoantibody precursors might contribute to a greater understanding of autoimmune phenomena in age and disease.

Selection of VH gene repertoires: differentiating B cells of adult bone marrow mimic fetal development

In the present study we have compared by in situ hybridization and by a CFU-B colony assay VH family usage in the pre-B and B cell compartments of the bone marrow of adult BALB/c and C57BL/6 mice. We have found that the position dependent increased expression of the VH 7183 family, observed in neonatal mice, is characteristic of early differentiating B cells of adult mice. The quantitative analysis for each VH family of the number of pre-B and B cells produced daily and the number of mature B cells present in the peripheral immunocompetent cell pool of adult BALB/c demonstrates the existence of selecting mechanisms operating within the bone marrow at the level of the emergent repertoire and at the level of export of newly formed cells into the periphery. This selective process results in the decreased peripheral representation of the VH 7183 family and in the accumulation of cells belonging to the other VH families. Selection of VH family usage in peripheral repertoires may be determined according to lymphocyte life-span, as we have found a preferential utilization of the VH J558 family in populations of partially enriched, long-lived B cells.

All T15 Id-positive antibodies (but not the majority of VHT15+ antibodies) are produced by peritoneal CD5+ B lymphocytes

After adult irradiation and reconstitution with autologous bone marrow, BALB/c and C.B20 mice no longer utilize the T15 Id in response to phosphorylcholine. T15 Id expression can be restored by transfers of peritoneal B cells or by FACS-purified CD5+ IgM+ lymphocytes (but not by T lymphocytes) from syngeneic donors. Using bone marrow and peritoneal cell donors that are congeneic for heavy and light chain allotypes, the exclusive origin of the T15 Id in peritoneal B cells was ascertained. These conclusions have been essentially confirmed by immunization with either anti-T15 Id or anti-VHT15 antibodies conjugated to lipopolysaccharide. Thus, the production of VHT15-positive antibodies continues at control levels in bone marrow-reconstituted animals while no T15 Id production can be stimulated even in this protocol of direct B cell stimulation. These results constitute the first formal demonstration of the exclusive production of and Id by CD5+ B-cells.

I-E-linked control of spontaneous rheumatoid factor production in normal mice

The concentration of serum IgM molecules binding to IgG2a (rheumatoid factor [RF]) in solid phase assays is 10-100-fold higher in normal, unmanipulated C3H/HeJ (H-2k) than in C57BL/6 (H-2b) mice. Analysis of MHC-congenic mice with the prototype strains show that C3H SW (H-2b) are low, and B6.H-2k are high RF expressor strains, respectively. Furthermore, segregation of RF phenotypes in progenies from backcrosses to C3H/HeJ of (C3H/HeJ x C57BL/6)F1 hybrid mice shows MHC- and IgH-linked controls. RF phenotypes also segregate as if they are MHC linked in crosses between H-2-congenic strains (C3H/HeJ and C3H.SW). The study of intra-H-2 (k/b and k/s) recombinant mice suggested that RF phenotype control is linked to the I-E region. This was confirmed by the typing of C57BL/6 mice expressing a transgenic E alpha chain, and thus, I-E+, which, in contrast to nontransgenic littermates, are high expressors of RF.