Adjunctive corticosteroid therapy in patients with pulmonary tuberculosis

OBJECTIVES

In tuberculosis treatment, corticosteroids are used as adjuvants, especially in meningeal/pericardial tuberculosis. In other forms of the disease, especially in severe tuberculosis requiring mechanical ventilation, its use is controversial. The aim of the present study is to assess whether the use of corticosteroids in the treatment of pulmonary tuberculosis patients in mechanical ventilation is associated with in-hospital mortality.

METHODS

This is a retrospective cohort study. Tuberculosis patients >18 years requiring mechanical ventilation, admitted to the emergency department or intensive care unit, were included. Data on corticosteroid use and mortality were collected.

RESULTS

In total, 467 patients were included in the analysis; 399 used corticosteroids and 68 were noncorticosteroid users. The mortality rate was higher among corticosteroid users (59.9%) than in noncorticosteroid users (41.2%) (p=0.010). The total dose of corticosteroid in prednisone equivalents was not different between survivors and nonsurvivors (median [interquartile range]: 80 mg [5-56.6 mg] vs. 80 mg [50-135 mg]; p=0.881).

CONCLUSIONS

Tuberculosis patients in mechanical ventilation who used corticosteroids had a higher mortality rate than those who did not use corticosteroids. The role of corticosteroids in pulmonary tuberculosis, especially in critically ill patients, remains unclear and needs further evaluation in prospective studies.

Post-tuberculosis lung disease: a comparison of Brazilian, Italian, and Mexican cohorts

Objective:

To evaluate lung function in a cohort of patients with a history of pulmonary tuberculosis in Brazil, as well as to evaluate the decline in lung function over time and compare it with that observed in similar cohorts in Mexico and Italy.

Methods:

The three cohorts were compared in terms of age, smoking status, pulmonary function test results, six-minute walk test results, and arterial blood gas results. In the Brazilian cohort, pulmonary function test results, six-minute walk test results, and arterial blood gas results right after the end of tuberculosis treatment were compared with those obtained at the end of the follow-up period.

Results:

The three cohorts were very different regarding pulmonary function test results. The most common ventilatory patterns in the Brazilian, Italian, and Mexican cohorts were an obstructive pattern, a mixed pattern, and a normal pattern (in 58 patients [50.9%], in 18 patients [41.9%], and in 26 patients [44.1%], respectively). Only 2 multidrug-resistant tuberculosis cases were included in the Brazilian cohort, whereas, in the Mexican cohort, 27 cases were included (45.8%). Mean PaO₂ and mean SaO₂ were lower in the Mexican cohort than in the Brazilian cohort (p < 0.0001 and p < 0.002 for PaO₂ and SaO₂, respectively). In the Brazilian cohort, almost all functional parameters deteriorated over time.

Conclusions:

This study reinforces the importance of early and effective treatment of drug-susceptible tuberculosis patients, because multidrug-resistant tuberculosis increases lung damage. When patients complete their tuberculosis treatment, they should be evaluated as early as possible, and, if post-tuberculosis lung disease is diagnosed, they should be managed and offered pulmonary rehabilitation because there is evidence that it is effective in these patients.

Do not underestimate the blood urea nitrogen-to-creatinine ratio in heart failure

Funding Acknowledgements

Type of funding sources: None.

Introduction

The blood urea nitrogen-to-creatinine ratio (BUN/SCr) has been proposed as a prognostic marker in heart failure (HF). We aimed to evaluate whether BUN/SCr predicts mortality outcomes in a real-world Southern European population with decompensated chronic HF.

Methods

We retrospectively studied 1057 patients with chronic HF admitted to our emergency department between November 2016 and December 2017 with acute decompensation. We excluded patients with a GFR &lt;15mL/min/m2 or on dialysis. The incidence of cardiovascular (CV) and all-cause death was evaluated through multivariable logistic regression models and by Kaplan-Meyer survival curves.

Results

1025 patients were included, median age 80 years (IQR 73-85), 52.4% male, mean LVEF 42.8 ± 12.7%, and mean GFR 57.2 ± 23.9 mL/min/m2. Mean BUN/SCr was 24.9 ± 8.2 and mean SBP was 139 ± 29mmHg (r=-0.17, p &lt; 0.001). After a median follow-up of 5 months (IQR 3-11 months), CV and all-cause death occurred in 8.0% and 21.6%, respectively. Mean BUN/SCr was higher in patients with fatal outcomes both for CV (31.3 vs. 24.3, p &lt; 0.001) and all-cause death (28.6 vs. 23.8, p &lt; 0.001). BUN/Scr was grouped by terciles: T1 (&lt;20.78), T2 (20.78-27.15), T3 (&gt;27.15). In the T3 group, the multivariable-adjusted  OR for CV and all-cause death was 5.43 (95% CI 2.20-13.37) and 2.72 (95% CI 1.66-4.46), respectively, compared to the T1 group. No significant differences between T1 and T2 groups.

Conclusions

BUN/SCr at admission predicts CV and all-cause death in patients with chronic HF after an episode of decompensation. BUN/SCr, as an easy-to-use tool, helps to identify those patients who benefit from tight monitoring both during hospitalization and after discharge.

Abstract Figure_1

Does lipoprotein(a) predict cardiovascular events in a long-term follow-up?

Funding Acknowledgements

Type of funding sources: None.

Background

Elevated plasma lipoprotein(a) [Lp(a)] concentrations are associated with an increased risk of atherosclerotic cardiovascular disease and its role in risk categorizing was recognized in the new ESC guidelines for the management of dyslipidaemias. We investigated 1) the association between baseline Lp(a) levels and incident long-term cardiovascular (CV) events and 2) its relationship with type 2 diabetes mellitus (T2DM) in a Southern European population.

Methods

We retrospectively assessed baseline Lp(a) concentrations in a total of 499 patients of a primary prevention cohort followed at the Lipidology Clinic of our hospital, with a median follow-up time of 15 (IQR 12-17) years. Lp(a) was analysed as a continuous variable, as a categorical variable with a 180mg/dL cut-off and by quartiles. We collected data on major CV events (CV death, myocardial infarction, stroke) as a composite outcome. Cox proportional hazard regression analyses were used to estimate hazard ratios (HR) and 95% confidence interval (CI).

Results

Mean age was 48.30 ± 14.41 years and 61.70% were male (n = 499). Median Lp(a) was 36.60 (IQR 0-396) mg/dL and 12.4% of patients had very high Lp(a) (≥180mg/dL); T2DM prevalence was 13.60%. The composite outcome incidence was 10%. At the baseline, individuals with T2DM had lower Lp(a) levels (11.85 IQR 3-330 mg/dL vs. 46.40 IQR 0-396, p &lt; 0.01 mg/dL). There was a moderate inverse correlation between Lp(a) and HbA1c (r = -0.67, p &lt; 0.01) but no significant correlations with lipid profile (total, LDL or HDL), risk scores (SCORE or the ACC pooled cohort equation), age nor gender. We found no relationship between baseline Lp(a) quartiles and composite outcome’s incidence (age-, sex-, and diabetes-adjusted HR: 1.15, 95%CI: 0.71-1.87, p = 0.57) (Figure 1), neither with the individual CV endpoints. Exploratory analysis showed that patients on aspirin had lower Lp(a) levels (29.55 IQR 0-264 mg/dL vs. 63.60 IQR 1-396 mg/dL, p &lt; 0.01).

Conclusion

In a single centre cohort of a primary prevention southern European population, we did not find an association between Lp(a) levels and incident CV events in a 15-year median follow-up time.

Myocardial infarction in young adults: are the risk profile and mortality outcomes different from older patients?

Funding Acknowledgements

Type of funding sources: None.

Introduction

The incidence of acute myocardial infarction (AMI) among young patients is increasing. The YOUNG-MI Registry reported that those under 40 years had similar risk profiles and outcomes compared to those aged 41 to 50. We aimed to evaluate cardiovascular risk factors and mortality outcomes in two age cohorts from southern European.

Methods

We retrospectively evaluated 4758 patients admitted to our coronary intensive care unit between 2004 and 2017 with AMI. We only included patients &lt;60 years in two subgroups: cohort A &lt; 50 years and cohort B 50-60 years. 

Results

From the 1233 patients included (mean age 50.5 ± 6.5 years, 82.2% male), 53% had STEMI. Cohort B had higher rates of hypertension (59.8 vs. 42.9%, p &lt; 0.001), diabetes (41.8 vs. 28.9%, p &lt; 0.001), and dyslipidemia (59.4 vs. 46.4%, p &lt; 0.001), while cohort A had higher rates of familial premature coronary artery disease (20.9 vs. 13.2%, p &lt; 0.001) and smoking habits (54.4 vs. 40.0%, p &lt; 0.001). Regarding coronary angiography, cohort B had higher rates of obstructive disease in each epicardial artery, except for left main involvement and non-obstructive disease (Fig. 1). Cohort A had lower all-cause mortality rates at the index hospitalization (1.3 vs. 3.2%, p = 0.045), 6-months (2.9 vs.5.4, p = 0.038), 1-year (3.1 vs. 6.3%, p = 0.014), and 3-years (3.6 vs 8.4, p = 0.001). After multivariable adjustment, we found no relationship between age cohorts and all-cause mortality for any follow-up timing: HR 1.57 (95% CI 0.56-4.37), 1.37 (95% CI 0.50-3.74), and 0.92 (95% CI 0.35-2.39) at 6-months, 1-year, and 3-years, respectively.

Conclusion

Among patients who suffer AMI, those under 50 years old have a different risk profile, compared to the 50-60 years cohort. However, there is no significant difference in all-cause mortality.

Abstract Figure.

Smoking prevalence and effects on treatment outcomes in patients with tuberculosis

OBJECTIVE

More than 20% of tuberculosis (TB) cases worldwide are attributable to smoking, and it is associated with an increased risk of latent and active TB, recurrence, and mortality. The aim of this study is to assess the smoking prevalence and the effects on treatment outcomes in TB patients.

METHODS

A prospective cohort study was conducted in patients with a recent TB diagnosis. The smoking status was defined, in addition to the patients' knowledge and attitudes toward smoking. The patients were followed up until the end of the treatment, and the treatment result was recorded.

RESULTS

Ninety-two patients were included in this study. The prevalence of active smoking was 31.5%. Active smokers had less chance for cure (62.1% versus 82.5%; p=0.032) and more treatment dropout (31.0% versus 12.7%; p=0.035) than non-active smokers. Patients demonstrated positive attitudes and good knowledge about smoking.

CONCLUSIONS

Active smokers had less chance for cure and more abandonment than non-active smokers. These results can be useful for the proper planning of actions that impact TB control, especially in the treatment results, such as cognitive-behavioral approaches to smoking cessation.

Tuberculosis in the intensive care unit: alternative treatment regimens and association with mortality

OBJECTIVES

Adequate anti-tuberculosis (TB) treatment is an important factor that can affect the patient's outcome. Higher mortality is found in patients who do not receive optimal treatment that includes isoniazid and rifampicin. The objective of this study is to evaluate the association of use of alternative TB treatment regimens (without rifampicin and isoniazid) and mortality among patients requiring intensive care.

METHODS

Retrospective cohort study, from January 2010 to December 2018. Patients aged > 18 years with a TB diagnosis, admitted to the ICU of a general, tertiary care, university-affiliated hospital (Hospital de Clínicas de Porto Alegre - HCPA) were included. Data on TB treatment used and outcomes of treatment were collected.

RESULTS

462 patients met the inclusion criteria and were included in the analysis; 284 used the usual treatment regimen (rifampicin, isoniazid, pyrazinamide and ethambutol - all orally), and 178 used alternative treatment regimens (IV levofloxacin plus oral ethambutol plus IM streptomycin or IV amikacin, without rifampicin and isoniazid). The mortality was higher among users of alternative treatment regimens (63.5%) than among usual treatment regimen users (51.4%) (P = 0.011). In a multivariate analysis, age, albumin and death were independently associated with alternative treatment regimens use.

CONCLUSIONS

TB programmes in which IV rifampicin is not widely available should consider including it, especially for critically ill TB patients, for whom there may be improved survival.

Tuberculosis in Health Care Workers and the Impact of Implementation of Hospital Infection-Control Measures

Background: Most studies that have evaluated the impact of infection-control measures (ICM) reported a decrease in latent tuberculosis (TB) and not in TB. The objective of this study was to evaluate the impact of ICM on TB incidence among Health Care Workers (HCW's). Methods: We conducted a retrospective record review study in a general, tertiary care, university-affiliated hospital. All TB case reports among HCWs in the hospital from 2005 to 2018 were reviewed. The TB incidence was measured before and after 2012 to evaluate the impact of ICM implemented. Findings: In total, there were 53 TB cases. The number of TB cases before and after the implementation of ICM was 42 (incidence: 100.0 cases/100,000 HCWs/year) and 11 (incidence: 26.2 cases/100,000 HCWs/year), respectively (p < .0001). Conclusions/Application to Practice: TB incidence among HCWs reduced significantly after the implementation of ICM. The establishment of ICM, such as written TB infection control plan, monitoring, screening, training, and education, can reduce TB incidence.

From lime to silica and alumina: systematic modeling of cement clinkers using a general force-field

Thirteen different cement-clinker crystalline phases present in the lime-silica-alumina system have been systematically modeled using a simple and general force field. This constitutes a new type of approach towards the study of lime-silica-alumina systems, where the simpler and more transferable Lennard-Jones potential was used instead of the more traditional Buckingham potential. The results were validated using experimental density and structural data. The elastic properties were also considered. Six amorphous phases (corresponding to calcium/silicon ratios corresponding to belite, rankinite, wollastonite and alumina-doped amorphous wollastonite with 5%, 10% and 15% alumina content) were also studied using molecular dynamics simulations. The obtained MD trajectories were used to characterize the different crystalline and amorphous phases in terms of the corresponding radial distribution functions, aggregate analyses and connectivity among silica groups. These studies allowed a direct comparison between the crystalline and amorphous phases and revealed how the structure of the silica network was modified in the amorphous materials or by the inclusion of other structural units such as alumina. The knowledge at an atomistic level of such modifications is paramount for the formulation of new cement-clinker phases.

Properties of nanoparticles prepared from NdFeB-based compound for magnetic hyperthermia application

Nanoparticles were prepared from a NdFeB-based alloy using the hydrogen decrepitation process together with high-energy ball milling and tested as heating agent for magnetic hyperthermia. In the milling time range evaluated (up to 10 h), the magnetic moment per mass at H = 1.59 MA m(-1) is superior than 70 A m(2) kg(-1); however, the intrinsic coercivity might be inferior than 20 kA m(-1). The material presents both ferromagnetic and superparamagnetic particles constituted by a mixture of phases due to the incomplete disproportionation reaction of Nd(2)Fe(14)BH(x) during milling. Solutions prepared with deionized water and magnetic particles exposed to an AC magnetic field (H(max) ~ 3.7 kA m(-1) and f = 228 kHz) exhibited 26 K ≤ ΔT(max) ≤ 44 K with a maximum estimated specific absorption rate (SAR) of 225 W kg(-1). For the pure magnetic material milled for the longest period of time (10 h), the SAR was estimated as ~2500 W kg(-1). In vitro tests indicated that the powders have acceptable cytotoxicity over a wide range of concentration (0.1-100 µg ml(-1)) due to the coating applied during milling.

Hierarchical classification of G-protein-coupled receptors with data-driven selection of attributes and classifiers

We address the important bioinformatics problem of predicting protein function from a protein's primary sequence. We consider the functional classification of G-Protein-Coupled Receptors (GPCRs), whose functions are specified in a class hierarchy. We tackle this task using a novel top-down hierarchical classification system where, for each node in the class hierarchy, the predictor attributes to be used in that node and the classifier to be applied to the selected attributes are chosen in a data-driven manner. Compared with a previous hierarchical classification system selecting classifiers only, our new system significantly reduced processing time without significantly sacrificing predictive accuracy.

Predicting Hydration Free Energies of Neutral Compounds by a Parametrization of the Polarizable Continuum Model

A parametrization of the polarizable continuum model (PCM) is presented having the experimental hydration free energies of 215 neutral molecules as target. The cavitation and dispersion contributions were based on the Tuñon-Silla-Pascual-Ahuir (Tuñon; et al. Chem. Phys. Lett. 1993, 203, 289) and Floris-Tomasi (Floris, F.; Tomasi, J. J. Comput. Chem. 1989, 10, 616) expressions, respectively. Both the polar and nonpolar contributions were evaluated on the same solvent-excluding molecular surface that used unscaled Bondi atomic radii. The parametrization was provided for the HF, Xalpha, LSDA, B3LYP, and mPW1PW91 methods at the 6-31G(d) basis set, and the results are in fair agreement with the experimental data. For the sake of comparison, the PCM(UAHF) and our parametrization (PCM2), both at HF level, have produced DeltaG(PCM(UAHF)) = aDeltaGexp (a = 1.02 +/- 0.02, r = 0.945, sd = 0.987, Ftest = 1778) and DeltaG(PCM2) = aDeltaGexp (a = 0.95 +/- 0.02, r = 0.952, sd = 0.843, Ftest = 2070), respectively. The mean absolute deviations from experimental data were 0.67 and 0.68 kcal/mol for PCM(UAHF) and PCM2, respectively.

CD8+ T lymphocytes in double alpha beta TCR transgenic mice. I. TCR expression and thymus selection in the absence or in the presence of self-antigen

We derived Rag2-deficient mice bearing two rearranged alphabeta TCR transgenes, one specific for the HY male Ag and the second specific for the gp33-41 peptide of lymphocytic choriomeningitis virus, both restricted to the MHC H-2D(b) class I molecule. We found that, in female double transgenic (DTg) mice, most CD8 T cells express only the TCRbeta chain from the aHY transgene. By comparing the mRNA species for both beta-chains, we observed that in T cells from DTg mice the aHY TCRbeta chain transcripts are abundant, whereas the anti-lymphocytic choriomeningitis virus TCRbeta chain transcripts are rare. In contrast to TCRbeta chain expression, most of the T cells from DTg mice express two TCRalpha chains. We examined the thymus selection of the dual-receptor CD8 T cells in the presence of self-Ag. We found that the presence of a second TCRalpha chain allows a significant number of CD8 T cells expressing a self-reactive receptor to escape central deletion and migrate to the peripheral pools of male mice. Differences in TCR and coreceptor expression between female and male MoaHY and DTg mice suggest that peripheral T cell survival requires an optimal level of signaling, which implies a process of "adaptation" of lymphocyte populations to the host environment.

CD8+ T lymphocytes in double alpha beta TCR transgenic mice. II. Competitive fitness of dual alpha beta TCR CD8+ T lymphocytes in the peripheral pools

We studied Rag2-deficient mice bearing two rearranged alphabeta TCR transgenes, both restricted to the MHC H-2D(b) class I molecule. We have previously shown that, in these DTg mice, most peripheral CD8 T cells express one TCRbeta chain associated with two TCRalpha chains, as in one-third of the mature T cells from normal mice. We examined the functional behavior of the dual-receptor CD8 T cells developing either in the absence or in the presence of self-Ag. The dual-receptor CD8 T cells, which develop in absence of self-Ag, show efficient responses to immunization and remain sensitive to induction of peripheral tolerance. In contrast to single TCR T cells, the dual-TCR cells, when tolerized upon exposure to high levels of self-Ag, are not deleted and therefore may exert important regulatory functions. When developing in the presence of self-Ag, the dual-receptor-expressing CD8 T cells escape central deletion, but are not fully competent to respond to cognate stimuli. Overall, we found that the dual-TCR CD8 T cells show a poor competitive value and can be out-competed by single-TCR cells, both in the course of immune responses and in reconstitution experiments. The decreased fitness of the dual-receptor cells may contribute to diminishing the autoimmune hazard that they could represent.

Resource competition determines selection of B cell repertoires

Previous experiments with mouse chimeras demonstrated that cellular competition for antigen-specific survival signals plays a crucial role in the maintenance of the naive B cell repertoire. Transgenic (Tg) B cell populations in these chimeras have a shortened lifespan and poor competitive abilities as compared to more diverse non-Tg populations in the same mice. We develop a mathematical model to investigate the mechanism of B cell competition. The model allows for various B cell clones, generated in the bone marrow, to go into the peripheral circulation, where they compete specifically for various ligands providing survival signals. In the model we also find the observed poor competitive abilities of the Tg repertoire. Investigating the nature of the competition in the model, we find that most of the competition is "intraspecific" occurring largely within the clone of truly Tg B cells, and within the repertoire of leaky Tg and non-Tg B cells. This is confirmed by analysing a simplified version of the model, which only allows for intraspecific competition, and resembles a simple ecological model with density-dependent death. The fact that our model accounts for the data, casts doubt on a previous interpretation of the same data arguing that more diverse repertoires outcompete repertoires of lower diversity. Here, we conclude that most of the data can be explained with intraspecific competition, and formulate an experimental prediction that allows one to distinguish between the previous interpretation of inter-specific competition between repertoires, and the current interpretation of intraspecific competition.

Peripheral B cell survival

Recent findings suggest that lymphocyte survival is a continuous active process and support the role of B cell receptor engagement in B cell survival. In this context the conflict of survival interests between the diverse B cells gives rise to a pattern of interactions which mimics the behavior of complex ecological systems. In response to competition lymphocytes modify their survival requirements and diverge to occupy different immunological niches through differentiation. Thus naive and memory-activated B cell populations show independent homeostatic regulation. We discuss how niche differentiation allows the coexistence of different cell types and guarantees both repertoire diversity and efficient immune responses.

B cell positive selection by self antigens and counter-selection of dual B cell receptor cells in the peripheral B cell pools

The presence of B cells expressing two B cell receptors (BCR), described in BCR-transgenic, gene-targeted and normal mice, may represent an autoimmune hazard. We generated RAG-2-deficient mice bearing two complete rearranged immunoglobulin transgenes. In these mice most mature resting B cells express chains from the two transgenes. We studied selection of these dual receptor B cells in the presence of self antigens. In spite of the reduced surface density of the anti-self receptor, self-reactive B cells are deleted in the presence of membrane-bound self antigens. In contrast, the presence of soluble self antigen positively selects single receptor B cells expressing the self-reactive receptor. At the periphery these positively selected B cells down-regulate surface IgM expression and become unresponsive. A few dual receptor cells, however, escape tolerance induction. We examined the peripheral fate of the dual receptor B cells and showed that they are poorly selected into the activated B cell compartment and show a poor competitive capacity when in presence of populations of single receptor B cells. These results indicate that peripheral selection contributes to the very low frequencies of dual receptor B cells in normal mice and that multiple safeguard mechanisms operate to minimize the autoimmune hazard that allelically included B cells could represent.

Population biology of lymphocytes: the flight for survival

In this essay we suggest that the primary goal of the cells of the immune system is to ensure their own growth and survival. In adults, in steady-state conditions, the number and distribution of lymphocyte populations is under homeostatic control. New lymphocytes that are continuously produced in primary and secondary lymphoid organs must compete with resident cells for survival. We discuss recent findings supporting lymphocyte survival as a continuous active process and implicating cognate receptor engagement as fundamental survival signals for both T and B lymphocytes. The conflict of survival interests between different cell types gives rise to a pattern of interactions that mimics the behavior of complex ecological systems. In their flight for survival and in response to competition, lymphocytes use different survival signals within different ecological niches during cell differentiation. This is the case for T and B lymphocytes and also for naive and memory/activated T and B cells. We discuss how niche differentiation allows the co-existence of different cell types and guarantees both repertoire diversity and efficient immune responses.

Peripheral T cell survival

T cell survival in the periphery is an active process, depending on continuous TCR engagement by peptide-MHC complexes and/or response to environmental cytokines. Naive T cells require interactions with the MHC restricting element. The survival requirements of memory T cells are as yet insufficiently characterized, but MHC-restricted interactions are not necessary.

Transfer of small resting B cells into immunodeficient hosts results in the selection of a self-renewing activated B cell population

We studied the role of bone marrow B cell production in the renewal of peripheral B cells and the feedback mechanisms that control the entry of newly formed B cells into the peripheral B cell pools. When resting lymph node B cells are injected into B cell-deficient hosts, a fraction of the transferred cells expands and constitutes a highly selected population that survives for prolonged periods of time by continuous cell renewal at the periphery. Although the number of donor B cells recovered is low, a significant fraction shows an activated phenotype, and the serum immunoglobulin (Ig)M levels are as in normal mice. This population of activated B cells is resistant to replacement by a new cohort of B cells and is able to feedback regulate both the entry of newly formed B cells into the peripheral pool and terminal differentiation. These findings suggest that peripheral B cell selection follows the first come, first served rule and that IgM-secreting cells are generated from a pool of stable activated B cells with an independent homeostasis.

The role of the B cell receptor V region in peripheral B cell survival

We investigate the role of the antigen-specific B cell receptor (BCR) in the establishment and maintenance of the peripheral B cell pools. We studied the fate of a population of transgenic B cells expressing a BCR without V region (Tg(deltaVmu)). We found that the Tg(deltaVmu) B cells can populate the peripheral B cell pools in the absence of other B cells, but when in the presence of a second population of non-transgenic B cells, they are virtually absent from the mature B cell compartments. By studying the rate of accumulation of 5-bromo-2'-deoxyuridine we show that the peripheral Tg(deltaVmu) B cells have a shorter life-span compared to non-transgenic B cells. By directly comparing the fate of two populations of transgenic B cells, either lacking or expressing a V region, we were able to assign the poorest competitive ability and the short peripheral survival of the Tg(delatVmu) B cells to the lack of an antigen-binding site. The results obtained support the involvement of the V region in the persistence of peripheral B cell populations.

Lymphocyte homeostasis

B- and T-lymphocyte populations have an independent homeostatic regulation of resting (B and T) and activated (B) or memory (T) cell compartments. This organization may provide an efficient mechanism to ensure simultaneously a first natural barrier of protection against common pathogens, the maintenance of immunological T-cell memory and a reservoir of repertoire diversity capable of dealing with new antigenic challenges.

Independent homeostatic regulation of B cell compartments

In the present study we used mice with a developmental arrest of B cell production to study the ability of a limited number of normal B cell precursors to populate peripheral B cell pools. In chimeras reconstituted with mixtures of bone marrow (BM) cells from normal and B cell-deficient donors, we show that the rate of BM B cell production is a constant function of the number of BM pre-B cells and is not modified by the peripheral B cell pool size, i.e. there is no feedback regulation of the central pre-B cell compartment by the number of mature B cells. We also show that the physiological number of peripheral B cells requires a minimum continuous input of newly formed cells, but is not determined by the number of B cell precursors. Chimeras with a threefold reduced rate of BM B cell production have normal numbers of peripheral B cells. Parabiosis between normal and B cell-deficient mice showed that the BM B cell production of one mouse suffices to replenish the B cell pool of three mice. Finally, we show that the compartment of activated IgM-secreting B cells is homeostatically autonomous since the number of cells it comprises is regulated independently of the size of the mature B cell pool. The results presented here support a model of the immune system in which the size of the different B cell compartments, i.e. pre-B, resting B and IgM-secreting, is autonomously regulated.

Differential requirements for survival and proliferation of CD8 naïve or memory T cells

The requisite molecular interactions for CD8 T cell memory were determined by comparison of monoclonal naïve and memory CD8(+) T cells bearing the T cell receptor (TCR) for the HY antigen. Naïve T cells required only the right major histocompatibility complex (MHC) class I-restricting molecule to survive; to expand, they also needed antigen. In contrast, for survival, memory cells did not require the restricting MHC allele, but needed only a nonspecific class I; for expansion the correct class I, but not antigen, was required. Thus, maintenance of CD8 T cell memory still required TCR-MHC class I interactions, but memory T cells may have a lower functional activation threshold that facilitates secondary responses.

Resource competition as a mechanism for B cell homeostasis

Cellular competition for survival signals offers a cogent and appealing mechanism for the maintenance of cellular homeostasis [Raff, M. C. (1992) Nature (London) 356, 397-400]. We present a theoretical and experimental investigation of the role of competition for resources in the regulation of peripheral B cell numbers. We use formal ecological competition theory, mathematical models of interspecific competition, and competitive repopulation experiments to show that B cells must compete to persist in the periphery and that antigen forms a part of the resources over which B cells compete.

Cellular competition modulates survival and selection of CD8+ T cells

In this investigation we compare the repopulation of the CD8+ T cell compartments of bone marrow (BM) chimeras by either normal nontransgenic or T cell receptor (TcR) alpha beta-transgenic (TG) CD8+ T cells, the fate of TG and non-TG CD8+ T cells in different parabionts and the survival of TG and non-TG peripheral CD8+ T cells after transfer into athymic hosts. We found that cellular competition among CD8 T cells occurs at several steps of T cell differentiation including a) during the DN to DP transition, b) positive selection in the thymus, c) export from the thymus and d) in the periphery. Comparison of the results obtained in the BM chimeras and in the parabionts shows that an important step of T cell selection occurs during seeding of peripheral lymphoid tissues. Once established, peripheral T cells resist replacement by recent thymus migrants, i.e. in the periphery, selection of T cell repertoires follows the rule "first come, first served". Peripheral dominance correlates with T cell activation and division. Cell cycling and CD44 expression are more frequent among non-TG CD8 T cells than TG CD8 T cells and within the latter, more frequent among P14 TG CD8 T cells than anti-HYTG CD8 T cells. Thus, in the absence of intentional immunization, the frequencies of CD8+ T cells follow a hierarchy of selection in which non-TG > or = P14 TG > anti-HY TG. We also show that the equilibrium size and the fate of one CD8 T cell population differs according to the presence or absence of other CD8 T cell populations. Under these circumstances, selection of T cell repertoires and T cell survival and memory rely not only on the interactions of each T cell with their respective ligands, but also on the nature and number of other competing cells.

Persistence of V beta 6+ T cells in Mls-1a mice. A role for the third complementarity-determining region (CDR3) of the T cell receptor beta chain in superantigen recognition

We have studied V alpha 2 and J beta usage by V beta 6+CD4+ peripheral T cells isolated from the congenic mice strains BALB/c (Mls-1b) and BALB.D2 (Mls-1a). We found that the TCR beta-chain of V beta 6+CD4+ T cells present in adult Mls-1a mice differed from those in Mls-1b mice; the fraction of V beta 6+CD4+T cells using the J beta 2.7 segment was reduced, while the number of V beta 6+CD4+ T cells using J beta 1.2 was augmented. These results indicate that the CDR3 region of the TCR beta-chain participates in recognition of the Mls superantigen. We also found that in Mls-1a mice an increased fraction of V beta 6+CD4+ T cells expressed the V alpha 2 chain. The study of J beta usage by V beta 6+CD4+V alpha 2+ and V beta 6+CD4+V alpha 2- T cells indicates that both J beta segment and TCR V alpha 2 chain expression confer complementary protection against deletion by Mls-1a superantigen. These results suggest a novel view of Mls-1a-driven selection, where the CDR3 region of the V beta chain modulates superantigen recognition, and the affinity/avidity of the TCR-MHC-superantigen complex determine the fate of the T cell.

Persistence of V beta 6+ T cells in Mls-1a mice. A role for the third complementarity-determining region (CDR3) of the T cell receptor beta chain in superantigen recognition

We have studied V alpha 2 and J beta usage by V beta 6+CD4+ peripheral T cells isolated from the congenic mice strains BALB/c (Mls-1b) and BALB.D2 (Mls-1a). We found that the TCR beta-chain of V beta 6+CD4+ T cells present in adult Mls-1a mice differed from those in Mls-1b mice; the fraction of V beta 6+CD4+T cells using the J beta 2.7 segment was reduced, while the number of V beta 6+CD4+ T cells using J beta 1.2 was augmented. These results indicate that the CDR3 region of the TCR beta-chain participates in recognition of the Mls superantigen. We also found that in Mls-1a mice an increased fraction of V beta 6+CD4+ T cells expressed the V alpha 2 chain. The study of J beta usage by V beta 6+CD4+V alpha 2+ and V beta 6+CD4+V alpha 2- T cells indicates that both J beta segment and TCR V alpha 2 chain expression confer complementary protection against deletion by Mls-1a superantigen. These results suggest a novel view of Mls-1a-driven selection, where the CDR3 region of the V beta chain modulates superantigen recognition, and the affinity/avidity of the TCR-MHC-superantigen complex determine the fate of the T cell.

External fixation of intertrochanteric fractures of the femur

Forty patients with intertrochanteric fractures of the femur were treated by external fixation between July 1992 and April 1994. They were selected because of their high surgical risk, and evaluated by radiographs immediately after operation, and at 30 and 90 days. The results indicate that external fixation is a useful method of treatment for this type of patient.

The role of cellular competition in B cell survival and selection of B cell repertoires

We studied the competitive repopulation by different B cells of irradiated mice reconstituted with bone marrow from either congenic or Ig-transgenic (TG) mice mixed at different ratios. We found that after reconstitution, the number of B cells recovered in the different chimeras is similar and independent of the ratio of injected cells. In chimeras hosting TG and non-TG cells, the relative representation of the donor cell lineages diverges from the ratios present in the inoculum, i.e. at the periphery, non-TG cells are preferentially selected. Selection of non-TG cells only occurs when population growth plateaus, i.e. when resources become limiting and competition starts to operate. Selection of non-TG cells depends on surface Ig expression, and they are selected because they have a longer survival. Finally, the life-expectancy of the same B cell population differs depending upon the second population present. The present results show that the life-span and the population size of each B cell clone can be altered (interfered with) by the presence of a second cell population, demonstrating the existence of cellular competition among B cells. Our findings establish the role of cellular competition in the selection of B cell repertoires and the existence of a hierarchy of B cell selection in the absence of antigenic stimulation. The implications of cellular competition on our understanding of the immune system are discussed.

Anergy and exhaustion are independent mechanisms of peripheral T cell tolerance

We studied the interactions of male-specific T cell receptor (TCR)-alpha/beta-transgenic (TG) cells with different concentrations of male antigen in vivo. We constructed mouse chimeras expressing different amounts of male antigen by injecting thymectomized, lethally irradiated mice with various ratios of male (immunoglobulin [Ig] Ha) and female (IgHb) bone marrow. These chimeras were injected with male-specific TCR-alpha/beta-trangenic cells. These experiments allowed us to monitor antigen persistence and characterize antigen-specific T cells in terms of their frequency, reactivity, and effector functions (as tested by elimination of male B cells in vivo). In the absence of antigen, virgin TG cells persisted but did not expand. Transient exposure to antigen resulted in cell expansion, followed by the persistence of increased numbers of antigen-reactive T cells. In contrast, antigen persistence was followed by two independent mechanisms of tolerance induction: anergy (at high antigen concentrations), where T cells did not differentiate into effector functions but persisted in vivo as unresponsive T cells, and exhaustion (at lower antigen concentrations), where differentiation into effector functions (B cell elimination) occurred but was followed by the disappearance of antigen-specific T cells.

Entry of B lymphocytes into the persistent cell pool in non-immunized mice is not accompanied by somatic mutation of VH genes

In this study we compare VH-gene repertoires of short-lived and persistent B lymphocytes in normal nonimmunized mice. Enriched populations of persistent peripheral B cells were obtained in vivo either by (i) repeated injections with hydroxyurea or (ii) maintained ganciclovir administration to herpes simplex virus-1 thymidine kinase transgenic mice. Both approaches have previously been shown to deplete newly formed, short-lived B cells. VH genes expressed by persistent or unselected B cell populations were amplified by polymerase chain reaction, cloned using the lambda-ImmunoZAP system (Stratagene) and sequenced. The results presented here concern a total of 116 complete VH sequences from two VH gene families of established germ-line composition: VH7183 and VHX24. No differences were found between the two cell populations as to usage of D or JH segments and to the presence of N sequence additions at D/JH or VH/DJH junctions and CDR3 length. Over 90% of the sequenced VH genes were of germ-line arrangement with no evidence of somatic mutation. These results show that persistent B cells in normal mice are not of embryonic origin and that somatic hypermutation is not necessary for B cell survival. They also suggest that a significant fraction of persistent IgM+ B cells in normal mice are not generated by conventional antigenic stimulation and could represent a novel class of "memory" cells expressing germ-line repertoires.

Regulation of VH-gene expression is a lineage-specific developmental marker

We have previously shown that in IgH congenic mice VH-gene family usage in neonatal spleen B cells and adult Ig-secreting cells is entirely determined by the IgH locus, while in adult resting B cells it is regulated by genetic element(s) located outside the IgH locus. Two observations reported here demonstrate that the differential expression of VH genes is an intrinsic property of the respective cell populations, determined by both the IgH locus and by a cis element(s) operating independently in the same animal. First, the study of F1 hybrids between the IgH congenic B6a and CB.20 strains demonstrates that cis elements control VH-gene family expression. Second, studies in irradiation chimeras showed that the environment in which cell differentiation proceeds is unable to overcome those controls. In chimeras of IgH congenic donors, VH-gene expression in fetal liver-derived splenic B cells and Ig-secreting cells is dictated by the IgH haplotype, while in bone marrow-derived B cells is entirely determined by the cis element(s). These results show a developmental and cell lineage-related restriction in VH-gene expression, and suggest that most adult splenic Ig-secreting cells may originate from precursors originally present in fetal liver, but which are rare among adult bone marrow precursors and CD5+ B cells.

VH-gene family dominance in ageing mice

The cellular composition and VH-gene family repertoire were compared in different B-cell compartments from young adult (8-12 weeks) and old (18-24 months) C57BL/6 and BALB/c mice. Ageing mice were found to have a higher frequency of peripheral mature B cells utilizing genes from a single VH-gene family. While in each individual old C57BL/6 mice cells expressing the VH J558 gene family consistently were over-represented, a marked individual variation was observed in old BALB/c mice with increased frequency of either the VH J558, Q52 or J606 families. Aged mice were found also to have a reduced number of bone-marrow pre-B cells and an augmented number of splenic Ig-secreting cells. These results suggest that old mice express less diversified antibody repertoires possibly as a consequence of reduced input from precursors and increased peripheral selection, which may be responsible for the progressive establishment of immunodeficiency.

V region dependent selection of persistent resting peripheral B cells in normal mice

In this study, we compare the VH gene family repertoire of persistent long-lived splenic B cells with that of the whole splenic B cell compartment. Persistent long-lived B cells were obtained by two independent strategies. Firstly, we studied cells that persist in the peripheral pools with or without cell division. We have transferred mature lipopolysaccharide (LPS)-reactive splenic B cells into LPS non-responder recipients and studied the donor population that could be recovered in host mice at differing time intervals after cell transfer. Secondly, we studied non-cycling resting long-lived B cells. These cells were obtained in normal mice after cytostatic treatment with hydroxyurea and in mice transgenic for the HSV-1 thymidine kinase gene after treatment with the anti-herpetic ganciclovir. Studying the VH gene family usage at the single level by in situ hybridization, we found that persistent B cells show an increased expression of the VHJ558 family and a diminished representation of the VH7183 family. These results demonstrate that in a normal non-immunized mouse, B cell survival and persistence in the resting state results from V region dependent selection.

Differential expression of VH gene families in peripheral B cell repertoires of newborn or adult immunoglobulin H chain congenic mice

The pattern of VH gene family expression in the primary B cell repertoire of the mouse is strain dependent. In C57Bl/6 mice, the VH J558 family is expressed by more than 45% of the cells, while the expression of VH 7183, VH Q52, and VH 36-60 families together does not exceed 20%. In BALB/c mice, relative expression of VH J558 is lower than 35%, while the sum of the other three families reaches 25%. To assess which genetic loci control strain-specific VH gene family expression, we studied VH gene family usage in splenic B cell repertoires of different congenic strains of mice. Changes in major histocompatibility complex or immunoglobulin (Ig) K light chain genes did not modify VH gene family expression in adult mice. Differences at the IgH locus, however, modified VH gene family usage. In 1-d-old mice, the strain-specific VH gene family expression pattern is determined by the IgH haplotype. In adult mice, the VH gene family expression pattern of resting B cells is independent of the IgH locus and follows the genetic background of the congenic strain, while it is determined by the IgH haplotype among Ig-secreting spleen cells. In F1(B6 x BALB/c) mice, each of the two spleen B cell populations, sorted on the basis of mu heavy chain allotype expression, shows an independent VH gene family expression pattern, determined by the IgH locus. The implications of these results in the control of VH gene family expression, and in the selection of peripheral B cell repertoires are discussed.

Clonal analysis of B lymphocyte responses to Plasmodium chabaudi infection of normal and immunoprotected mice

Parasite infection causes marked perturbations in the host immune system, as shown by hypergammaglobulinemia, autoimmunity and immune depression, but there is little information on the number, specificities and performance of B cell clones activated in the course of infection. We have addressed these questions in a model of murine malaria induced by Plasmodium chabaudi, where primary infection results in very marked B cell responses that shift in Ig isotype pattern in immunoprotected animals, and where immunity can be transferred to naive recipients by injection of serum from late, but not early, infection. We have quantitated B cells responding to infection in two distinct functional compartments, namely blast cells and Ig-secreting cells, and compared normal with immune animals. We have also determined the frequencies of clonal specificities towards several autoantigens (DNA, myosin, transferrin and red cells), non-self protein or polysaccharide antigens (KLH, levan and dextran), and parasite antigens in both compartments, by measuring blast cell reactivities in limiting dilution analyses and Ig secretion in ELISASPOT assays. This experimental design allowed us to assess the specificity of the B cell responses, to compare the clonal composition of these two B cell compartments, and to evaluate putative specific response regulation at the step of terminal differentiation. Our results show that, in this particular experimental system: (i) B cell responses in primary infection are truly non-specific while immune animals show a greater ability to control the massive non-specific response; (ii) parasite specific B cells, particularly those committed to IgG production, are selectively stimulated in immune individuals; (iii) autoreactive B cells are not selectively stimulated, but increased autoantibody production may result from perturbation in the control of terminal differentiation in the respective clones; (iv) clones with specificity to some non-self antigens (e.g. KLH and dextran) are selectively engaged and regulated, which might have implications for the immunosuppression following infection.

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.

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.

Transfer of T or CD8+ cells from hemorrhaged mice produce alterations in bacterial antigen specific plasma cell repertoires in normal syngeneic recipients

Hemorrhage has multiple effects on immunologic response, including alteration of B cell repertoires and T cell function. This study examined possible relationships between these two phenomena by determining the effects of T cells and T cell subsets transferred from hemorrhaged donors into normal, unhemorrhaged syngeneic recipients on B cell repertoires. Mice given total T or CD8+ cells from hemorrhaged animals then immunized with the bacterial polysaccharide antigen levan had a decreased percentage of plasma cells producing antibody to levan compared to that in mice given T or CD8+ cells from unhemorrhaged animals. These effects of post hemorrhage CD8+ cells were not seen after transfer into nu/nu mice, indicating that these cells did not directly affect B cell function, but rather required other T cell populations in order to alter the B cell repertoire. These results demonstrate that hemorrhage-induced alterations in bacterial antigen specific B cell repertoires may result from T and CD8+ cell mediated changes in T-B interactions.

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.

Immunoglobulin VH gene expression following hemorrhage

Hemorrhage has multiple effects on immunologic response, including alteration of B cell repertoires. In limiting dilution studies, decreased absolute frequencies of splenic clonal precursors specific for bacterial antigens were found after blood loss. In order to better define the effects of hemorrhage on B cell function, we examined immunoglobulin VH gene family expression following blood loss using both in situ hybridization and the RNA colony blot technique. No changes in VH gene family utilization were found after hemorrhage. These results demonstrate that the hemorrhage induced alteration in B cell function involves all VH gene families, without modifying distributive frequencies in VH gene family expression.

Accumulation of bromodeoxyuridine-labeled cells in central and peripheral lymphoid organs: minimal estimates of production and turnover rates of mature lymphocytes

Daily lymphocyte production in both central and peripheral lymphoid organs was evaluated by associating in vivo incorporation of bromodeoxyuridine (BrdUrd) with cell surface labeling and multi-parameter flow analysis. At least 10% of mature T and B lymphocytes are generated every 24 h. The kinetic behavior of these cell populations differs, however, in that mature B cells are generated predominantly in the precursor compartments of the bone marrow, while most mature T cell generation occurs at the periphery. Therefore, peripheral expansion is the major mechanism of mature T cell production in the adult mouse. By following the accumulation of BrdUrd-labeled cells in peripheral lymphoid organs we found that the progeny of the daily lymphocyte production was sufficient to renew 30%-40% of all peripheral T and B cells every 48 h, demonstrating a high turnover rate of mature lymphocytes. We also examined the conditions of BrdUrd labeling of cycling cells in vivo. We found that while greater than 90% of bone marrow and thymus cells in S phase were labeled with a single injection of BrdUrd, in peripheral lymphoid compartments 70% of T and B cells in S failed to incorporate BrdUrd. Particular schedules of BrdUrd administration were required to overcome the low labeling efficiency of mature cells in vivo. Prolonged BrdUrd administration, however, had toxic effects on resident cells. The low labeling efficiency of BrdUrd incorporation by mature cells, as well as its potential toxicity during prolonged administration, may explain controversial results obtained by the different strategies used to study lymphocyte population dynamics.

VH gene family repertoires of "viable motheaten" (mev) mice

Mutant viable motheaten (mev) mice provide an useful experimental model to study the origin and molecular properties of autoantibodies. In the present investigation we have compared by in situ hybridization VH gene family usage in lipopolysaccharide-activated B cells (available repertoire) and spontaneously immunoglobulin-secreting (actual repertoire) B cells in the spleen of 6-8-week-old BALB/c and mutant BALB/c-mev mice. We have found that while sharing identical available splenic repertoires and expressing a diversified set of VH families, mev mice differ from control BALB/c animals in VH family representation in the actual plasma cell repertoires where they showed a decreased utilization of VH7183 genes and an increased representation of the VHJ606 family when compared to control BALB/c animals. These results indicate that selection of actual repertoires may indeed differ between autoimmune and control mice, but do not establish whether such changes are the primary cause of the disease or whether they are secondary to the initiating of the autoimmune process.