A model for developmentally acquired thymus-dependent tolerance to central and peripheral antigens

Current models of tolerance to peripheral, tissue-specific antigens contain some major caveats. First, they consider peripheral tolerance independently from intrathymic T cell selection, a dichotomy that is challenged by observations on TE-induced tolerance. Second, they do not account for the fact that vertebrates are more readily tolerised in development than in adult life. Third, they do not explain the fact that embryonic/neonatal tolerance to foreign tissues can only be induced by HC or TE. A model of thymic selection and peripheral tolerance is developed here that resolves those problems, by assuming two classes of T cell effector functions, one being regulatory and the other aggressive. Three postulates are required: (1) both epithelial and hemopoietic cellular compartments of the thymic stroma can support both positive and negative selection of T cells, but with vastly different avidity requirements and efficiency; (2) positively selected T cells with the highest avidity that escape deletion are activated intrathymically and irreversibly committed for regulatory effector functions; (3) the functional phenotype of all other thymic emigrants is determined in the periphery upon encounter with antigen. Functional commitment in the periphery depends on the maturity stage (RTE or PMR) of the immunocompetent cell, on the nature of the antigen-presenting cells, and on the effector classes of other T lymphocytes interacting on the same presenting cell. This model explains a number of observations on experimental autoimmune disease and transplantation tolerance, and it contains several readily testable predictions.

Evidence for a thymus-dependent form of tolerance that is not based on elimination or anergy of reactive T cells

The avian embryo has provided an appropriate model to study the ontogeny of the primary lymphoid organs, thymus and bursa of Fabricius. By using the quail-chick marker system the embryonic origin of the highly intricate cell components which form these organs could be traced back to the initial endodermal, mesodermal and ectodermal germ layers. The timing and dynamics of the incoming and outcoming flows of hemopoietic cells which characterize their lymphopoietic activity could be revealed in both quail and chick embryos. This knowledge served as a basis for an investigation on the role of the epithelial component of the thymus (derived from the pharyngeal endoderm) on tolerance to tissue graft and, by extension, tolerance to self. When this work was undertaken, the prevailing view was that exposure of the developing immune system to foreign antigens in the embryo allows them to be assimilated to self components in the mature animal. In fact, this was found to be true for allogeneic grafts between MHC-distinct chickens, of certain tissues, such as for instance wing tissues. However, in heterospecific transplantations, i.e. when a limb bud was grafted from quail to chick embryos, the chick host acutely rejected the foreign limb soon after birth. In contrast, grafts of the quail thymic epithelial (TE) rudiment resulted in the development of a chimeric thymus in which the foreign epithelial component was not only tolerated but able to induce full tolerance of the grafted wing from the same donor. By monitoring the amount of quail TE implanted we showed in addition that only part of the peripheral T-cell population had to differentiate in the context of the quail epithelial cells to induce tolerance to quail tissues. This pointed to the generation in the thymus of regulatory T cells, coexisting with specific anti-quail reactive T cells, but able to inhibit them from reacting against the quail wing antigenic determinants. A mammalian model was then devised to further study this mechanism of tolerance that we have qualified as "dominant" by opposition to the current model based on either clonal elimination or anergy which can be considered as recessive or passive. Nude mice of MHC type A were grafted with TE of E10 type B embryos. They became reconstituted for T-cell function but tolerant for B skin allografts. Spleen cells from such tolerant animals injected to naive A nude mice reconstituted T cell function in the recipient and transferred the tolerance to B skin grafts. Reducing the number of donor cells resulted in the segregation of the two phenomena. For low numbers the recipients were restored but not tolerant, thus showing the coexistence in the tolerant donor of anti-B reactive T cells together with regulatory cells able to abolish their reactivity against B determinants. Other experiments demonstrated that TE-induced tolerance does not rely on clonal deletion or anergy. This was shown on systems where elimination of cells directed toward superantigens was screened. It turned out that tolerance to skin grafts and superantigen T-cell deletion are unrelated phenomena. These observations strongly suggest that tolerance to self results at least in part from the interplay between cells potentially harmful for self component and others which exert a strong control on their reactivity. The latter cell type depends upon interactions of thymocytes with the endodermal component of the thymus.

B-lineage cell deficits in bone marrow of lpr/lpr mice

Analyses of bone marrow (BM) lymphocytes in C57BL/6 mice homozygous for the lpr mutation (B6.lpr) disclosed low numbers of pre-B and B cells, as compared with age-matched control B6 mice. BM depletion in B6.lpr mice was selective for B-lineage cells, appeared in young adults, and developed markedly with age and disease progression, contrasting with the peripheral lymphocyte hypercellularity. Normalization of pre-B and B cellularity in BM of B6.lpr mice was observed after administration of polyclonal Ig, that also markedly improved the clinical condition. Isolated pre-B (B220+ IgM-) cells from B6 or B6.lpr mice, however, showed essentially the same rates of IL-7-dependent proliferation and differentiation to B (IgM+) cells in culture, indicating that the BM B-lineage deficit is not the result of an intrinsic defect in B cell generation.

Murine acariasis: I. Pathological and clinical evidence suggesting cutaneous allergy and wasting syndrome in BALB/c mouse

We describe here a disease related to mite-associated ulcerative dermatitis in BALB/c mice, a strain previously classified as resistant to this condition. The disease was recognized by pruritic cutaneous pathology and wasting. Pathologic studies showed a marked allergic-type inflammation in the skin. The dominant histologic feature was extensive mast cell infiltration in cutaneous lesions and in lymphoid tissues, associated with a greatly elevated serum IgE concentration. The disease was secondary to infestation with an acarian ectoparasite Myocoptes musculinus, and seemed to represent an allergic reaction to the parasite-derived substances, with an associated wasting syndrome. This condition may be a useful experimental model for allergic diseases.

Rearrangement and expression of Vzeta1, Vzeta2 and Vzeta3 TCR zeta genes in C57BL/6 mice

We have recently described a mAb (2.11) that recognizes the Vgamma1-Jgamma4-Cgamma4 chain. With this mAb and an anti-delta mAb we separated gammadelta+ 2.11(+) and gammadelta+ 2.11(-) intraepithelial lymphocytes (i-IEL) by FACS. Transcripts of rearranged TCR Vgamma1 and Vdelta2 genes in both i-IEL populations were analyzed by PCR followed by sequence analysis of cDNA spanning the junction of variable (V) and joining (J) genes. Roughly the same number of Vgamma1 and Vgamma2 transcripts were found in the 2.11(+) population while >90% of the transcripts in the 2.11(-)population contained a Vgamma gene sequence. Furthermore, gamma transcripts in the 2.11+ population were functional, while only 30-40% of the Vgamma transcripts in either population contained an in-frame sequence. The observed frequency of transcripts is what would be expected from cell populations that have not gone through cellular selection mediated by the RCR. Expression of Vgamma mRNA in RCRalphabeta and TCRgammadelta thymocytes was studied by a technique that analyzed populations of transcripts of rearranged genes. In both T cell population similar levels of Vgamma transcripts were found and about two out of three transcripts were out-of-frame. During the cloning and sequence analysis, we indentified a clone that expresses the Vgamma segment rearranged to the Jgamma3-Cgamma region in C57BL/6 mice. Together with the PCR cloning and sequencing of the complete Cgamma region in C57BL/6 mice these data demonstrate that the Jgamma-Cgamma gene is functional in this strain. Taken together, these studies revealed that: (i) cells expressing the Vgamma1 chain are an important subset of the gammadelta i-IEL population and that they show extensive junctional diversity; (ii) there is no correlation between expression of in-frame Vgamma transcripts and expression of Vgamma2 chains at the cell surface; and (iii) cells expressing the Vgamma3 chain might be a minor subset of the gammadelta T cell population in C57BL/6 mice.

Occurrence of living adult Wuchereria bancrofti in the scrotal area of men with microfilaraemia

To determine the frequency with which living adult Wuchereria bancrofti can be detected by ultrasound in the scrotal area of men with filarial infection, we used a 7.5 MHz transducer to perform weekly ultrasound examinations on 100 microfilaraemic men (18-34 years old) from Greater Recife, Brazil. The peculiar pattern of movement that characterizes the adult worm image on ultrasound (the filaria dance sign) was detected in the lymphatic vessels of the spermatic cord in 80 men (bilaterally in 29 men). Among 20 men with no filaria dance sign, the geometric mean microfilarial density was 68/mL, compared with 238/mL and 775/mL among those with unilateral and bilateral filaria dance signs, respectively (P = 0.0001). The lymphatic vessels of the spermatic cord appear to be a common, and perhaps the principal, site of adult W. bancrofti in men with asymptomatic microfilaraemia. Studies are needed to define the relationship between the presence of filarial worms in the scrotal area and the development of filaria-associated morbidity.

Self-association of the polyene antibiotic nystatin in dipalmitoylphosphatidylcholine vesicles: a time-resolved fluorescence study

The interaction between Nystatin and small unilamellar vesicles of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, both in gel (T = 21 degrees C) and in liquid-crystalline (T = 45 degrees C) phases, was studied by steady-state and time-resolved fluorescence measurements by taking advantage of the intrinsic tetraene fluorophore present in this antibiotic. It was shown that Nystatin aggregates in aqueous solution with a critical concentration of 3 microM. The enhancement in the fluorescence intensity of the antibiotic was applied to study the membrane binding of Nystatin, and it was shown that the antibiotic had an almost fivefold higher partition coefficient for the vesicles in a gel (P = (1.4 +/- 0.1) x 10(3)) than in a liquid-crystalline phase (P = (2.9 +/- 0.1) x 10(2)). Moreover, a time-resolved fluorescence study was used to examine Nystatin aggregation in the membrane. The emission decay kinetics of Nystatin was described by three and two exponentials in the lipid membrane at 21 degrees C and 45 degrees C, respectively. Nystatin mean fluorescence lifetime is concentration-dependent in gel phase lipids, increasing steeply from 11 to 33 ns at an antibiotic concentration of 5-6 microM, but the fluorescence decay parameters of Nystatin were unvarying with the antibiotic concentration in fluid lipids. These results provide evidence for the formation of strongly fluorescent antibiotic aggregates in gel-phase membrane, an interpretation that is at variance with a previous study. However, no antibiotic self-association was detected in a liquid-crystalline lipid bilayer within the antibiotic concentration range studied (0-14 microM).

Natural autoantibodies

Autoantibodies of the IgM, IgG and IgA classes, reactive with a variety of serum proteins, cell surface structures and intracellular structures, are 'naturally' found in all normal individuals. Present in human cord blood and in 'antigen-free' mice, their variable-region repertoire is selected by antigenic structures in the body and remains conserved throughout life. Encoded by germline genes with no, or few, mutations, natural autoantibodies are characteristically 'multireactive' and do not undergo affinity maturation in normal individuals. Natural autoantibodies may participate in a variety of physiological activities, from immune regulation, homeostasis and repertoire selection, to resistance to infections, transport and functional modulation of biologically active molecules.

Regulatory T cells in thymic epithelium-induced tolerance. I. Suppression of mature peripheral non-tolerant T cells

Athymic mice grafted at birth with allogeneic thymic epithelium (TE) display life-long tolerance to tissue grafts of the TE donor strain, in spite of harboring peripheral T cells capable of rejecting those grafts. Tolerance is maintained in these chimeras by TE-specific regulatory CD4 T cells. We presently address the quantification and the mechanisms of this dominant tolerance process. C57BL/6 mice containing variable but defined numbers of peripheral, resident T cells received cell transfers of graded numbers of peripheral T cells from B6(BALB E10) chimeras (C57BL/6 nude mice grafted with TE from 10-day-old BALB/c embryos), resulting in a series of animals containing a wide range of donor (tolerant) versus host (non-tolerant) T cell chimerism. Increasing the relative representation of donor T cells results in a progressive delay in the rejection of BALB/c skin grafts, life-long tolerance being achieved at a ratio of tolerant and non-tolerant T cell populations of 1. In recipients displaying full tolerance, graft-reactive non-tolerant T cells were not deleted, anergized or committed to noninflammatory functions. Thus, sorted host T cells from tolerant recipients readily rejected BALB/c skin grafts upon transfer to immunodeficient animals. Finally, measurements of "helper" and inflammatory activities, as well as interleukin-4 and interferon-gamma production, failed to discriminate between T cell populations from tolerant and non-tolerant animals after specific in vitro stimulation. We conclude that: (a) TE-selected regulatory T cells can suppress, in a quantitative manner, in vivo T cell responses against major and minor histocompatibility antigens expressed by the TE and, (b) this suppressive activity neither inactivates mature non-tolerant T cells, nor does it seem to drive their differentiation along noninflammatory pathways.

Analysis of the natural human IgG antibody repertoire: life-long stability of reactivities towards self antigens contrasts with age-dependent diversification of reactivities against bacterial antigens

We used a quantitative immunoblotting technique to analyze the repertoires of IgG antibody reactivities in the serum of healthy young children, young adult males and aged males with self and non-self antigens. Densitometric patterns of reactivity of purified IgG with self antigens were highly conserved between individuals within a given age group and across age groups. Inter-individual differences were observed, however, upon analysis of self reactivities of IgG in whole serum. A striking heterogeneity between individuals within a given age group and across age groups characterized the reactivity of purified IgG and of IgG in whole serum with bacterial antigens. Inter-individual differences were more marked among aged individuals than among individuals of other age groups. Analysis of variances of reactivities of IgG with bacterial antigens further demonstrated an increased diversity of repertoires of aged donors compared with those of young adults and children. Our results document the stability of the self-reactive repertoires of IgG throughout life, which contrasts with the diversification of the repertoire of IgG antibody reactivities directed toward foreign antigens with aging. These findings support the concept that self-reactive antibody repertoires are positively selected throughout life by a restricted set of self antigens shared by all individuals.

Lymphocytes selected in allogeneic thymic epithelium mediate dominant tolerance toward tissue grafts of the thymic epithelium haplotype

Athymic mice grafted at birth with allogeneic thymic epithelium (TE) from day 10 embryos before hematopoietic cell colonization reconstitute normal numbers of T cells and exhibit full life-long tolerance to skin grafts of the TE haplotype. Intravenous transfers of splenic cells, from these animals to adult syngeneic athymic recipients, reconstitute T-cell compartments and the ability to reject third-party skin grafts. The transfer of specific tolerance to skin grafts of the TE donor strain, however, is not observed in all reconstituted recipients, and the fraction of nontolerant recipients increases with decreasing numbers of cells transferred. Furthermore, transfers of high numbers of total or CD4+ T cells from TE chimeras to T-cell receptor-anti-H-Y antigen transgenic immunocompetent syngeneic hosts specifically hinder the rejection of skin grafts of the TE haplotype that normally occurs in such recipients. These observations demonstrate (i) that mice tolerized by allogeneic TE and bearing healthy skin grafts harbor peripheral immunocompetent T cells capable of rejecting this very same graft; and (ii) that TE selects for regulatory T cells that can inhibit effector activities of graft-reactive cells.

The ontogeny of class-regulation of CD4+ T lymphocyte populations

The differential class-regulation of CD4+ T lymphocyte populations is believed to play a major role in determining the qualitative behaviour of the immune system, and in the fate of immune responses in particular. In this article we propose a model for the dynamics of the Th1 and Th2 subpopulations. We put forward the concept of an 'antigenic niche' which allows us to postulate that the key feature underlying the regulation of Th differentiation pathways is the population dynamics of the lymphocytes themselves. Using this model we are able to account for a number of well established experimental observations which were hitherto apparently unrelated and poorly understood. This suggests that our simplified model might be capturing some essential features of the immune system.

The network theory: 21 years later

The network theory was proposed 21 years ago, attracting then much interest as applied to the regulation of (clonal) immune responses. The first 10 years of 'idiotypic network' research have thus addressed questions that were already appropriately solved by the clonal selection theory, leading to a justifiable loss of its impact. In contrast, 'second generation networks', concentrate on systemic properties that emerge from a network organization, thus providing a framework for several major questions that seem to supersede clonal solutions: the developmental 'learning' of self antigenic composition and the maintenance of the respective 'memory' (self-tolerance), repertoire selection and the homeostatic regulation of lymphocyte numbers, natural immune activities that are independent of external antigens, the physiology of autoreactivity. The immune network may well contribute solutions to autoimmune diseases, where clonal approaches, classical and modern alike, have failed.

Direct assessment of the adulticidal efficacy of a single dose of ivermectin in bancroftian filariasis

Although the potent microfilaricidal activity of ivermectin is well established, its efficacy against adult Wuchereria bancrofti is unknown. We used longitudinal ultrasound examinations for periods of 3-9 months to assess directly the macrofilaricidal effect of a single 400 micrograms/kg dose of ivermectin in 15 men from Recife, Brazil who were infected with W. bancrofti. Before treatment, microfilarial densities ranged from 3 to 3098 microfilariae per mL of blood, and movements characteristic of the living adult worm (the 'filaria dance sign') were observed by ultrasound examination of the scrotal lymphatic vessels in all 15 men. Following treatment, microfilarial density was markedly reduced in all men, but the filaria dance sign remained unchanged in both location and pattern. Eight months after treatment, a dilated lymphatic vessel was surgically removed from one patient at the site of the filaria dance sign, and 3 intact adult worms were released. When given as a single 400 micrograms/kg dose, ivermectin had no observable effect on adult W. bancrofti. Therefore, prolonged suppression of microfilaraemia following treatment with ivermectin cannot be explained by a macrofilaricidal effect of the drug. Ultrasound is a valuable new tool for directly and rapidly assessing the macrofilaricidal efficacy of antifilarial drugs in lymphatic filariasis.

Analysis of the normal human IgG antibody repertoire. Evidence that IgG autoantibodies of healthy adults recognize a limited and conserved set of protein antigens in homologous tissues

We have used a quantitative immunoblot technique to analyze the Ab repertoire of IgG in the serum of healthy adults with a large panel of homologous and foreign Ags in tissue extracts. Densitometric patterns of reactivity of purified IgG with self-Ags exhibited striking homogeneity among individuals with regard to the protein bands that were recognized. Purified IgG showed higher levels of reactivity with self-Ags than IgG in whole serum. Reactivity with self-Ags of IgG in whole serum was restricted to a small number of protein bands (fewer than 10). There were significant inter-individual differences in the intensity and nature of immunoreactivities. Purified IgG of different individuals exhibited heterogeneous patterns of immunoreactivity with Ags in bacterial extracts. Comparative analysis of repertoires of IgG and IgM indicated that all protein Ags recognized by IgM were also reactive with purified IgG. Some proteins in homologous and in foreign tissue extracts reacted solely with IgG. Our observations provide direct evidence for the restricted and conserved character of the antiself-repertoire of IgG of healthy adults and suggest that natural IgG Ab repertoires in serum are specifically selected for reactivity with a limited set of self-Ags. In addition, IgG autoreactivity in whole serum is controlled by non-IgG factors that determine the unique reactivity pattern of each individual.

Analysis of the normal human IgG antibody repertoire. Evidence that IgG autoantibodies of healthy adults recognize a limited and conserved set of protein antigens in homologous tissues

We have used a quantitative immunoblot technique to analyze the Ab repertoire of IgG in the serum of healthy adults with a large panel of homologous and foreign Ags in tissue extracts. Densitometric patterns of reactivity of purified IgG with self-Ags exhibited striking homogeneity among individuals with regard to the protein bands that were recognized. Purified IgG showed higher levels of reactivity with self-Ags than IgG in whole serum. Reactivity with self-Ags of IgG in whole serum was restricted to a small number of protein bands (fewer than 10). There were significant inter-individual differences in the intensity and nature of immunoreactivities. Purified IgG of different individuals exhibited heterogeneous patterns of immunoreactivity with Ags in bacterial extracts. Comparative analysis of repertoires of IgG and IgM indicated that all protein Ags recognized by IgM were also reactive with purified IgG. Some proteins in homologous and in foreign tissue extracts reacted solely with IgG. Our observations provide direct evidence for the restricted and conserved character of the antiself-repertoire of IgG of healthy adults and suggest that natural IgG Ab repertoires in serum are specifically selected for reactivity with a limited set of self-Ags. In addition, IgG autoreactivity in whole serum is controlled by non-IgG factors that determine the unique reactivity pattern of each individual.

Studies on the T cell dependence of natural IgM and IgG antibody repertoires in adult mice

The present experiments address the thymic dependence of IgM and IgG natural antibody repertoires in adult euthymic and athymic BALB/c mice, as well as in athymic animals reconstituted with a fixed number of syngeneic T cells. Within 3 weeks of the transfer of 10(7) syngeneic splenic T lymphocytes to athymic mice, the T cell compartment is essentially reconstituted in the peritoneal cavity (up to 80% of the numbers in euthymic animals), but is only 10-20% of controls in the spleen and lymph nodes. Early after transfer, there is an increase in the numbers of activated B cells and of immunoglobulin-secreting cells in the spleen, and within 1-2 weeks, the serum concentrations of IgG1 and IgG2a are fully reconstituted to control levels (30-40-fold increased). Multiparametric analyses of serum IgM and IgG repertoires revealed that euthymic and athymic mice share essentially all natural antibody reactivities towards syngeneic extracts of liver and muscle. When tested at the same immunoglobulin concentrations, however, nude sera consistently show higher values of reactivity in all detectable bands. The transfer of 10(7) splenic T cells into athymic mice results in a general decrease of serum IgM reactivities, some of which become undetectable, and in alterations of the serum IgG repertoire as early as 1 week, and for at least 4 weeks after transfer. T cell transfer, however, fails to restore the euthymic IgM and IgG repertoires within 4 weeks. The present observations demonstrate that, after limited T cell reconstitution of nude mice, there is a rapid and quantitatively important increase of serum IgG1 and IgG2a production; the serum IgM reactivity repertoire is qualitatively similar in euthymic and athymic animals, but is generally decreased by T cell activity; and the serum IgG repertoire, which is qualitatively similar in euthymic and athymic animals, is amplified by T cell activity and partially altered by T cell transfer into athymic animals. These results raise questions on the mechanisms of B cell activation and natural antibody repertoire selection in T cell-deficient adult individuals.

Simple developmental programs of gene expression and cellular composition of lymphoid organs at the origin of natural tolerance

Self-tolerance is acquired in the embryonic/perinatal period, but new lymphocytes (that will have to distinguish between self and nonself) continue to be produced throughout life, after both self and nonself are present. This makes it impossible for natural tolerance to rely on recessive mechanisms. Recent observations on "dominant tolerance" have led to the hypothesis that natural tolerance is established as a consequence of simple developmental programs for gene expression and cellular composition of primary lymphoid organs. In development, the cellular composition of the thymus is predominantly epithelial, allowing for the positive selection and activation of "high avidity" self-reactive T cells that are not deleted because antigen presentation by haemopoietic cells is limiting. Such T cells, activated in that environment, display effector functions of a regulatory type that are maintained in the periphery upon restimulation by tissue peptides shared with the thymic epithelium. Recent thymic emigrants with specificity for tissue-specific antigens that are absent from the thymus will first encounter their ligands in the context of the "regulatory cell" recognition of ubiquitous peptides and are thus recruited into similar regulatory activities. In contrast, thymic emigrants with specificity for nonself antigens (absent during the perinatal period) are not activated intrathymically, reach the periphery as resting cells, and move out of the time window of susceptibility to functional recruitment. These will react "de novo" upon encounter of the respective antigens and will acquire the class of effector functions determined by the peripheral microenvironment in which they are activated. This strategy, which explains the thymic dependence of peripheral tissue-specific tolerance, may be re-enforced by developmental restrictions in cytokine gene expression, and it will ensure the establishment and maintenance of T-cell tolerance through the dynamic storage of a distributed memory of the embryonic self. B lymphocytes that are produced in the embryonic/perinatal period characteristically rearrange and express a few V-genes very predominantly. These V-genes encode antibodies with unique properties of "connectivity" to other V-regions, making it possible to establish a network that limits clonal expansions and/or terminal differentiation to antibody production. Self-reactive B cells are thus recruited into such a network which, by contributing to the molecular environment of the body and to the selection of emergent repertoires, leads to deletion of connected cells and to the "normalization" of the adult antibody repertoires. Natural autoantibody repertoires in the adult are thus recursively maintained, stable and continuously adjusted to the thresholds of single cell deletion and to the alterations in the body composition. The activity of self-specific regulatory T cells contributes to limiting clonal expansion and inhibiting somatic mutation of self-reactive B cells. This model explains a number of observations that were not included in the "clonal" and "recessive" tolerance views, and offers suggestions on mechanisms in physiological autoimmunity and pathology.

Comparative efficacy of three different diethylcarbamazine regimens in lymphatic filariasis

To assess the efficacy of diethylcarbamazine (DEC) in clearing Wuchereria bancrofti microfilariae (mf) from the circulation, we conducted a single blind hospital-based therapeutic trial of 3 DEC regimens. All patients were assessed by filtration of 1 mL of venous blood taken before and 1, 3, 6 and 12 months after DEC administration. The efficacy of a 12 d course of 6 mg/kg DEC once daily was identical to that of a similar course with 2 mg/kg given 3 times daily, indicating that split-dose treatment does not improve mf clearance over single daily drug administration. Microfilarial densities in patients treated only once with 6 mg/kg DEC remained significantly higher at 1, 3, and 6 months after treatment. However, all 3 treatment regimens proved equally effective in controlling microfilaraemia after 12 months, when 41, 42 and 40% of patients in the 3 treatment groups were amicrofilaraemic. These results suggest that a single DEC dose of 6 mg/kg administered annually or biannually may be a suitable regimen to control bancroftian filariasis in Recife, Brazil.

Invariance and restriction toward a limited set of self-antigens characterize neonatal IgM antibody repertoires and prevail in autoreactive repertoires of healthy adults

Analysis of the reactivity of IgM with self-antigens in tissues by a quantitative immunoblotting technique showed striking invariance among newborns in the human and in the mouse. The self-reactive repertoire of IgM of adults was also markedly conserved; it comprised most anti-self reactivities that prevailed among neonates. Multivariate analysis confirmed the homogeneity of IgM repertoires of neonates toward self- and non-self-antigens. Multivariate analysis discriminated between newborn and adult repertoires for reactivity with two of five sources of self-proteins and with non-self-antigens. Our observations support the concept that naturally activated B lymphocytes are selected early in development and throughout life for reactivity with a restricted set of self-antigens.

Thymic epithelium induces full tolerance to skin and heart but not to B lymphocyte grafts

Athymic nude mice reconstituted at birth with allogeneic thymic epithelia (TE) from day 10 embryos (E10), show life-long specific tolerance to skin and heart grafts, but eliminate B lymphocytes of the TE donor haplotype, nearly as well as those from a third strain. Previous immunizations with B cells do not alter the state of tolerance to skin grafts, but specifically accelerate elimination of lymphocytes. In contrast, transplantation of E15 allogeneic thymuses already seeded by hematopoietic cells resulted in chimeras tolerant to both skin and B lymphocytes. In vitro reactivities towards stimulator spleen cells of the haplotype of the thymus were observed in both E10 TE and E15 thymus chimeras. We conclude that induction of full in vivo tolerance to B cells requires hematopoietic cells, while this is not the case for induction of tolerance to skin and heart tissues; furthermore, in vitro reactivity to stimulator spleen cells of the tolerized haplotype is independent of in vivo tolerance.

Treatment of bancroftian filariasis in Recife, Brazil: a two-year comparative study of the efficacy of single treatments with ivermectin or diethylcarbamazine

The effectiveness of single oral doses of ivermectin (200 or 400 micrograms/kg) and diethylcarbamazine (DEC, 6 mg/kg), preceded 4 d earlier by either placebo or very small doses of these drugs, was compared, over a 2-year period, in a double-blind trial in 67 microfilaraemic Brazilian men with bancroftian filariasis. Regimens containing ivermectin alone decreased the number of microfilariae significantly faster and more effectively for the first month after treatment than regimens containing DEC alone, but the latter were significantly more effective throughout the second year after treatment (1.7-8.2% of pretreatment levels with DEC vs. 12.6-30.8% with ivermectin during that period); the higher ivermectin dose showed a tendency towards more effectiveness than the lower dose. Most effective was the combination of ivermectin (20 micrograms/kg) followed 4 d later by DEC (6 mg/kg), with reduction of microfilaraemia to 2.4% of pretreatment levels at 2 years. Adverse reactions were well tolerated with all regimens, the reactions being significantly more generalized (i.e., fever) following ivermectin and localized (i.e., scrotal inflammatory nodules around dying adult worms) following DEC. Further trials of single-dose combination therapy vs. single high doses of ivermectin or DEC should determine the ideal regimen for treatment and control of bancroftian filariasis.

Analysis of natural and disease-associated autoantibody repertoires: anti-endothelial cell IgG autoantibody activity in the serum of healthy individuals and patients with systemic lupus erythematosus

The present study demonstrates that natural IgG with anti-endothelial cell activity is present in the serum of healthy individuals and in pooled normal human Ig. By using a novel method that allows for the simultaneous and quantitative assessment of reactivities of antibodies with a large number of antigens in tissues, we observed that natural anti-endothelial cell antibody (AECA) recognizes a restricted set of self antigens in endothelial cells that is conserved among healthy individuals. The extent to which natural AECA activity is expressed in serum and the pattern of reactivity of AECA with endothelial cell antigens showed little variability between individuals. Analysis of AECA in the serum of patients with systemic lupus erythematosus (SLE) revealed a higher amount of activity and a wider spectrum of antigenic specificities than that recognized by natural antibodies in endothelial cell extracts. AECA activity of IgG in whole serum was lower than that of purified IgG in the case of healthy individuals and showed little variation among individuals. In contrast, no difference was found between AECA activity of purified IgG and that of IgG in patients' serum suggesting that SLE sera lack the factors that control expression of AECA activity in the serum of healthy individuals. Our results indicate that natural autoantibodies recognize a restricted and conserved set of self antigens. Our observations further suggest that defective regulation of the expressed autoreactive B cell repertoire is the basis for expansion of novel clonal specificities and enhanced autoantibody activity in serum of patients with autoimmune disease.

Leukocytes of patients with Schistosoma mansoni respond with a Th2 pattern of cytokine production to mitogen or egg antigens but with a Th0 pattern to worm antigens

Cytokine responses of peripheral blood mononuclear cells from humans infected with Schistosoma mansoni were assessed. By ELISA and ELISPOT, persons with acute and hepatosplenic infections produced higher levels of interleukin (IL)-4 and IL-5 and higher frequencies of IL-4-producing cells in response to mitogen than did uninfected persons. In contrast, mitogen-induced production of the Th1 cytokine interferon-gamma (IFN-gamma) did not differ from that of uninfected controls. Upon stimulation with egg antigens, many patients responded with elevated IL-4 mRNA levels but displayed no appreciable increases in Th1 (i.e., IFN-gamma and IL-2) cytokine transcripts. Nevertheless, in cells stimulated with adult worm antigen, a more mixed Th0-type response was observed with production of both Th1 and Th2 cytokines. These results support previous findings in laboratory mice that schistosome infection results in increased production of Th2 cytokines. Unlike mice, infected humans do not display a generalized down-modulation in Th1 responses but instead show a selective deficiency in IFN-gamma and usually IL-2 responses to egg antigens.