Efficacy and safety of high-flow nasal cannula therapy in elderly patients with acute respiratory failure

INTRODUCTION

To assess the efficacy and safety of high-flow nasal cannula (HFNC) in elderly patients with acute respiratory failure (ARF) not due to COVID-19, refractory to treatment with conventional oxygen therapy and/or intolerant to noninvasive ventilation (NIV) or continuous positive airway pressure (CPAP) and without criteria for admission to intensive care units (ICU).

METHODS

Prospective observational study of patients with ARF treated with HFNC who presented clinical and arterial blood gas deterioration after 24 h of medical treatment and oxygenation by conventional systems. The degree of dyspnoea, gas exchange parameters (arterial O2 pressure/inspired O2 fraction ratio (PaO2/FiO2); oxygen saturation measured by oximetry/ inspired fraction of oxygen (Sp02/Fi02), ROX index), degree of patient tolerance and mortality were evaluated. These were measured at discharge from the emergency department (ED), 24 h after treatment with conventional oxygenation and 60, 120 min and 24 h after initiation of HFNC. The results were analyzed for all patients as a whole and for patients with hypercapnia (arterial carbon dioxide tension (PaCO2) < 45 mmHg) separately.

RESULTS

200 patients were included in the study between November 2019 and November 2020, with a mean age of 83 years, predominantly women (61.9%), obese (Body Mass Index (BMI) 31.1), with high comorbidity (Charlson index 4) and mild-moderate degree of dependence (Barthel 60). A number of 128 patients (64%) were hypercapnic. None had respiratory acidosis (pH 7.39). Evaluation at 60 min, 120 min and 24 h showed significant improvement in all patients and in the subgroup of hypercapnic patients with respect to baseline parameters in respiratory rate (RR), dyspnoea, ROX index, PaO2/FiO2, SpO2/FiO2 and patient comfort. No changes in PaCO2 or level of consciousness were observed. HFNC was well tolerated. Ten patients (5%) died due to progression of the disease causing ARF.

CONCLUSIONS

HFNC is an effective and safe alternative in elderly patients with ARF not due to COVID-19, refractory to treatment with conventional oxygen therapy and/or intolerant to NIV or CPAP and without criteria for admission to ICU.

Predictors and outcomes of disseminated tuberculosis in an intermediate burden setting

SETTING

University-affiliated hospital located in Porto, North Portugal, an area with a low to intermediate incidence of tuberculosis (TB).

OBJECTIVE

To identify predictors and outcomes of disseminated TB (dTB).

DESIGN

A cohort of patients diagnosed with TB between 2007 and 2013 was retrospectively analysed. Patients with dTB criteria were characterized and compared to single organ TB cases. Factors independently associated with dTB were determined by multivariate logistic regression analysis.

RESULTS

A total of 744 patients were analysed, including 145 with dTB. Independent risk factors for dTB were pharmacological immunosuppression (OR 5.6, 95% CI 2.8-11.3), HIV infection (OR 5.1, 95% CI 3.1-8.3), chronic liver failure or cirrhosis (OR 2.3, 95% CI 1.4-4.1) and duration of symptoms (OR 2.3, 95% CI 1.4-3.8). Compared to single organ TB, the clinical presentation of dTB patients differed by the absence of haemoptysis (OR 3.2, 95% CI 1.3-8.4) and of dyspnoea (OR 1.9, 95% CI 1.2-3.1), presence of weight loss (OR 1.8, 95% CI 1.1-2.9), night sweats (OR 1.7, 95% CI 1.1-2.7) and bilateral lung involvement (OR 4.4, 95% CI 2.8-7.1). Mortality and time until culture conversion were higher for dTB patients, although not reaching statistical significance.

CONCLUSION

Immunosuppressive conditions and chronic liver failure or cirrhosis were associated with increased risk of dTB. The haematogenous spread may be dependent on longer symptomatic disease and usually progresses with bilateral lung involvement.

Epidemiology of traumatic brain injury in the elderly over a 25 year period

OBJECTIVE

To identify the changes in the epidemiology of traumatic brain injury (TBI) in a cohort of patients older than 65 years old admitted in the Intensive care unit of a third-level hospital over a 25 year period.

MATERIAL AND METHODS

A retrospective cohort study conducted on patients over 65 years-old admitted with the diagnosis of TBI into an intensive care unit of a Spanish university hospital. The demographic, clinical variables were collected at the time of admission, including comorbidities, injury mechanisms, and injuries presented, and days of stay in ICU. A statistical analysis was carried out by five-year periods.

RESULTS

A total of 446 TBI in patients over 65 years were included. In the analysis, an increase was observed in the proportion of patients presenting with epidural haematoma (1.39% in the period 1990-1995 vs. 9.46% in 2010-2015), with a significant linear tendency (P=.018). Falls from own height have increased from 8.33% (1991-1995) to currently more than 70% (2011-2015), P<.001. The percentage of traffic accidents declined from 26.39% to 3.95% in the last period, P<.001.

CONCLUSIONS

In the last 25 years there seems to be evidence of a change in the origins of TBI in the elderly in our field.

Osteogenic differentiation of two distinct subpopulations of human adipose-derived stem cells: an in vitro and in vivo study

The first stem cells considered for the reconstruction of bone were bone marrow mesenchymal stem cells (BMSCs). Subsequently, cells with similar marker expression panel and differentiation potential were found in new sources of cells, such as adipose tissue. This source of stem cells has a promising future in tissue-engineering applications, considering the abundance of this tissue in the human body, the easy harvesting and the high number of stem cells that are available from such a small amount of tissue. The isolation of the adipose stem cells is generally performed by means of enzymatic digestion of the tissues, followed by a natural selection of the stem cells based on their capacity to adhere to the culture flasks, leading to a quite heterogeneous population. This constitutes a major drawback for the use of these cells, since the heterogeneity of the cell culture obtained can compromise their proliferation and differentiation potential. In the present study we have analysed the in vitro and in vivo behaviour of two selected subpopulations with high osteogenic potential. For this purpose, ASCs(CD29+) and ASCs (STRO-1+)subpopulations were isolated and in vitro cultured onto a biodegradable polymeric scaffold, using osteogenic medium, before implantation in a nude mice model. The biodegradable polymeric scaffold used is a fibre-mesh structure based on a blend of starch and polycaprolatone (SPCL) that has been successfully used in several bone tissue-engineering studies. The implanted ASCs-scaffold constructs promoted the formation of new bone tissue in nude mice. However, the results obtained show differences in the behaviour of the two ASCs subpopulations under study, particularly regarding their potential to differentiate into the osteogenic lineage, and allowed the indentification of ASCs (STRO-1+) as the best subpopulation for bone tissue-engineering applications.

[Recombinant factor VIIa (rFVIIa). Description of use in a cohort of critical patients and prognostic markers]

OBJECTIVE

Describe and identify the factors associated with the survival of the patients who received treatment with rFVIIa in an Intensive Care Unit (ICU).

DESIGN

Longitudinal, ambispective, observational, descriptive study in a series of clinical cases performed from July 20, 2004 to July 20, 2006.

SCOPE

The study population included 16 hospitalized patients in the Intensive Medicine Department (ICU) of the Hospital Marqués de Valdecilla (Santander).

PATIENTS

Inclusion criteria were: Patients who required rFVIIa at some time of their stay in the ICU.

RESULTS

Hemodynamic improvement of the patients treated with rFVIIa in an ICU, within the first 3 hours of the infusion (evaluated by an increase of SBP > 20 mmHg and/or increase of DBP > 8 mmHg) was associated to greater survival.

CONCLUSIONS

The present series of cases, with the disadvantage of its heterogeneity and the limited number of patients, stresses the role of hemodynamic improvement as a differentiating factor between those patients who survive and those who do not.

Analysis of the immune response to Neospora caninum in a model of intragastric infection in mice

To study experimental Neospora caninum infection initiated at the gastrointestinal tract, Toll-like Receptor 4- and functional IL-12Rbeta2 chain-deficient C57BL/10 ScCr mice were challenged intragastrically with 5 x 10(6) N. caninum tachyzoites. All parasite-inoculated mice eventually died with disseminated infection. In contrast, immunocompetent BALB/c mice challenged with 1 x 10(7) N. caninum tachyzoites by the intragastric (i.g.) or the intraperitoneal (i.p.) route remained alive for at least 6 months. Expansion of splenic B- and T-cells, the latter displaying both activated and regulatory phenotypes, and increased levels of IFN-gamma and IL-10 mRNA were detected in both groups of infected BALB/c mice compared with non-infected controls, whereas in the Peyer's patches only IFN-gamma mRNA levels were found to be increased. Parasite-specific IgG1, IgG2a and IgA antibody levels were elevated in the sera of all infected mice, whereas increased N. caninum-specific IgA levels were detected in intestinal lavage fluids of i.g. challenged mice only. These results show that N. caninum infection can be successfully established in mice by i.g. administration of tachyzoites. They also show that the immune response elicited in i.g. or i.p. infected BALB/c mice, although conferring some degree of protection, was not sufficient for complete parasite clearance.

[Severe lactic acidosis associated to metformin intoxication]

Metformin is a biguanide extensively used in the treatment of type II diabetes mellitus. Between the nocive effects of the metformin emphasizes tha lactic acidosis because of its low frecuency but potential severity. The diagnosis of the poisoning due to metformin is based on the coexistence of lactic acidosis and one or more of the risk factors. The development of lactic acidosis in metformin poisoning is associated to a range of 50-80% of mortality.

Pericarditis purulenta y empiema pleural por Streptococcus pneumoniae

We present the case of a 59 year old woman with no previous clinical history of disease who was admitted in our ICU due to respiratory failure and hemodynamic instability. She was found to have purulent pericarditis due to Streptococcus pneumoniae, complicated by massive pericardial effusion and pleural empyema. A pericardial tap was performed unsuccessfully and finally pericardial effusion was evacuated by surgical drainage. Pleural empyema was also evacuated. She received antibiotic treatment and recovered with normalisation of heart function.

Neospora caninum: high susceptibility to the parasite in C57BL/10ScCr mice

C57BL/10ScCr mice, lack Toll-like receptor 4 and a functional Interleukin-12 receptor. Taking this into account, susceptibility of these mice to Neospora caninum infection was assessed comparatively to that of immunocompetent C57BL/10ScSn mice. C57BL/10ScCr mice inoculated intraperitoneally with 5x10(5)N. caninum tachyzoites showed a high susceptibility to this parasite. All infected C57BL/10ScCr mice were dead by day 8 post-infection whereas all control C57BL/10ScSn mice survived this parasitic challenge. Immunohistochemical analysis of infected C57BL/10ScCr mice showed N. caninum tachyzoites spread in the pancreas, liver, lung, intestine, heart and brain whereas no parasites were detected in similarly infected C57BL/10ScSn controls. The higher susceptibility of C57BL/10ScCr mice to neosporosis correlates with reduced interferon-gamma mRNA expression and increased IL-4 mRNA expression, comparatively to C57BL/10ScSn controls, detected in the spleen after the parasitic challenge. C57BL/10ScCr mice could thus be used as a new experimental model where to study immunobiological mechanisms associated with host susceptibility to neosporosis.

[Herpetic encephalitis in adults: 23 cases]

OBJECTIVE

To study the clinical presentation, diagnosis, treatment and prognosis of the herpetic encephalitis in our environment.

MATERIAL AND METHOD

During the past 12 years, 23 adults (age > 15 years) were treated for herpetic encephalitis in our centre.

RESULTS

There were 14 males and 9 females. Ages ranged from 18 to 84 years (mean, 52.30 +/- 18.64 years). The hospital stay ranged from 5 to 64 days (mean, 26.74 +/- 15.41 days). Eleven patients were managed in the intensive care unit and nine patients required mechanical ventilation. The most frequent clinical features they were the level of conscience decrease and fever. The lymphocytic pleiocytosis was the most frequent discovery in cerebrospinal fluid. The temporal lobe lesions in the computed tomography scan appeared in 14 patients (61%). Four patients died, seven patients were asymptomatic or with minimum sequels and twelve patients developed they were disabled.

CONCLUSIONS

The herpetic encephalitis is an uncommon illness. Intravenous acyclovir is recommended treatment and the corticosteroids use is controverted. The delay in the treatment beginning worsens the prognosis. Less than a third of the patients achieve the functional independence to discharge hospital.

Anti-interleukin 10 receptor monoclonal antibody is an adjuvant for T helper cell type 1 responses to soluble antigen only in the presence of lipopolysaccharide

Soluble foreign antigen usually leads to a transient clonal expansion of antigen-specific T cells followed by the deletion and/or functional inactivation of the cells. As interleukin (IL)-10 is a key immunoregulatory cytokine, we questioned whether neutralization of IL-10 during priming with soluble antigen could prime for a subsequent T helper cell type 1 (Th1) effector recall response. By using an adoptive transfer model to track the fate of antigen-specific T cell receptor (TCR)-transgenic CD4(+) T cells, we show that administration of soluble ovalbumin (OVA) protein, but not OVA(323-339) peptide antigen, together with an anti-IL-10 receptor (R) mAb led to the enhancement of a Th1 response upon rechallenge. Lipopolysaccharide (LPS) present in the protein was necessary for priming for Th1 recall responses in the presence of anti-IL-10R mAb, as removal of LPS abrogated this effect. Moreover, addition of LPS to the peptide did not itself allow priming for recall Th1 effector responses unless endogenous levels of IL-10 were neutralized with an anti-IL-10R mAb. A significant increase in OVA-specific IgG1 and IgG2a isotypes was observed when the protein antigen was administered with anti-IL-10R mAb; however, this was not the case with peptide antigen administered together with anti-IL-10R and LPS. Our data, showing that LPS receptor signaling and neutralization of endogenous immunosuppressive cytokines is essential for Th1 priming, has important implications for the design of relevant vaccines for effective in vivo immunotherapy.

Molecular and functional characterization of mouse signaling lymphocytic activation molecule (SLAM): differential expression and responsiveness in Th1 and Th2 cells

Optimal T cell activation and expansion require engagement of the TCR plus costimulatory signals delivered through accessory molecules. SLAM (signaling lymphocytic activation molecule), a 70-kDa costimulatory molecule belonging to the Ig superfamily, was defined as a human cell surface molecule that mediated CD28-independent proliferation of human T cells and IFN-gamma production by human Th1 and Th2 clones. In this study, we describe the cloning of mouse SLAM and the production of mAb against it which reveal its expression on primary mouse T and B cells. Mouse SLAM is expressed on highly polarized Th1 and Th2 populations, and is maintained on Th1, but not on Th2 clones. Anti-mouse SLAM mAb augmented IFN-gamma production by Th1 cells and Th1 clones stimulated through the TCR, but did not induce IFN-gamma production by Th2 cells, nor their production of IL-4 or their proliferation. Mouse SLAM is a 75-kDa glycoprotein that upon tyrosine phosphorylation associates with the src homology 2-domain-containing protein tyrosine phosphatase SHP-2, but not SHP-1. Mouse SLAM also associates with the recently described human SLAM-associated protein. These studies may provide new insights into the regulation of Th1 responses.

[Correlation between sensitivity of the cytogenetic and cytological analysis and thoracoscopic findings in the study of malignant pleural effusions]

We studied 104 patients with pleural effusion. All underwent thoracoscopic exploration to allow direct examination of any pleural lesions present. At the same time pleural biopsies for histopathologic study and samples of pleural fluid for cytopathologic and cytogenetic study were taken. The volume of fluid in pleural cavity was also measured. The aims of the study were: a) to evaluate the sensitivity of cytogenetic analysis and cytopathology, both separately and together, and b) to look for a correlation between the sensitivity of these cell studies and the following thoracoscopic findings: tissue biopsy of pleural neoplasms, volume of pleural effusion and extension of neoplastic lesions in the pleural cavity. Seventeen of the pleural liquids studied were benign and 87 were neoplastic. Cytopathology was sensitive in 55% of the neoplastic cases and cytogenetic study was sensitive in 49%. Sensitivity rose to 74% when both techniques were applied. Cytogenetic study yielded a higher percentage of correct diagnoses in the group with hematologic neoplasia, whereas cytopathology was correct more often in cases of solid tumors, though these differences were not statistically significant. Use of both techniques resulted in correct diagnosis in 92% of patients with mesotheliomas. The number or correct diagnoses achieved with cytopathology tended to increase with size of macroscopic pleural lesion whereas cytogenetic study was more sensitive in patients with minimal or incipient pleural involvement. There were no statistically significant differences in sensitivity of cytopathology and cytogenetic analysis with regard to volume of pleural effusion.

Susceptibility of beige mice to Mycobacterium avium: role of neutrophils

The beige mutation in C57BL/6 mice has been shown to increase the susceptibility to infection by Mycobacterium avium. In this study, we confirmed those results and showed that the effect of the beige mutation was most obvious after infection with a strain of lower virulence than with a highly virulent isolate of M. avium. The dissemination of M. avium from the gut was observed with both C57BL/6 and beige mice but was faster in the latter. The expression of gamma interferon (IFN-gamma) and the priming for tumor necrosis factor production during an in vivo infection were similar between beige and immunocompetent C57BL/6 mice. IFN-gamma produced during the infection of beige mice was protective in the spleen, and the administration of recombinant IFN-gamma restored the resistance in the spleen to levels similar to those found in control mice. There were no histological differences between wild-type and beige mice with respect to granuloma formation in the liver. The increased susceptibility of beige mice to M. avium as manifested in the liver was reduced by transfusing neutrophils from wild-type C57BL/6 mice. Likewise, depletion of neutrophils from C57BL/6 mice rendered them as susceptible to M. avium infection of the liver as beige mice. Our results point to the participation of neutrophils in the defect of beige mice in addition to other defects. Furthermore, these results show that neutrophils play a significant role in the defense mechanisms against mycobacterial infections and that beige animals may be a useful model for study of the role of neutrophils in mycobacteriosis.

Endogenously produced IL-12 is required for the induction of protective T cells during Mycobacterium avium infections in mice

Immunity to Mycobacterium avium depends on the induction of protective CD4+ T cells. In mice, M. avium induces a Th1 response leading to protective immunity dependent on IFN-gamma and TNF. In this study, we analyzed whether endogenously produced IL-12 was involved in the generation of such protective T cells. We found that the neutralization of IL-12 with the administration of specific mAbs throughout the course of the infection led to the inability of BALB/c mice to control the infection by M. avium strain 2447. On the contrary, the late neutralization of IL-12, with the administration of the mAb starting only at the third week of infection, did not affect the growth of M. avium. The neutralization of IL-12 blocked the induction of protective T cells detected upon adoptive transfer to sublethally irradiated recipient mice. The neutralization of IL-12 in the recipient mice did not affect the protective activity of immune cells, showing that IL-12 is involved mainly in the induction, and not the expression, of acquired cell-mediated immunity. IL-12 was also shown to be required for a T cell-independent pathway of resistance present in T cell-deficient severe combined immunodeficient (SCID) mice. Finally, animals whose IL-12 was blocked expressed heightened levels of IL-4 and IL-10 message and reduced expression of IFN-gamma as compared with control mice.

Endogenously produced IL-12 is required for the induction of protective T cells during Mycobacterium avium infections in mice

Immunity to Mycobacterium avium depends on the induction of protective CD4+ T cells. In mice, M. avium induces a Th1 response leading to protective immunity dependent on IFN-gamma and TNF. In this study, we analyzed whether endogenously produced IL-12 was involved in the generation of such protective T cells. We found that the neutralization of IL-12 with the administration of specific mAbs throughout the course of the infection led to the inability of BALB/c mice to control the infection by M. avium strain 2447. On the contrary, the late neutralization of IL-12, with the administration of the mAb starting only at the third week of infection, did not affect the growth of M. avium. The neutralization of IL-12 blocked the induction of protective T cells detected upon adoptive transfer to sublethally irradiated recipient mice. The neutralization of IL-12 in the recipient mice did not affect the protective activity of immune cells, showing that IL-12 is involved mainly in the induction, and not the expression, of acquired cell-mediated immunity. IL-12 was also shown to be required for a T cell-independent pathway of resistance present in T cell-deficient severe combined immunodeficient (SCID) mice. Finally, animals whose IL-12 was blocked expressed heightened levels of IL-4 and IL-10 message and reduced expression of IFN-gamma as compared with control mice.

Tumour necrosis factor-alpha (TNF-alpha) in the host resistance to mycobacteria of distinct virulence

The relative virulence of different isolates of Mycobacterium avium has been linked to their capacity to trigger the secretion of TNF from the macrophages they infect. Smooth opaque (SmOp) variants of Myco. avium have been shown to trigger higher expression of TNF-alpha by macrophages in vitro than the smooth transparent (SmTr) variants. To analyse the role of TNF in resistance to infection by Myco. avium, we studied the infection by two different morphotypes of strain 2.151 of Myco. avium both in vitro and in vivo in the presence or absence of neutralizing antibodies to TNF. No effects were found in vitro regarding the growth of either isolate of Myco. avium. In vivo, only the virulent SmTr morphotype showed enhanced growth in the presence of the neutralizing antibodies. This enhancement occurred relatively late when priming for TNF secretion in vivo was evident. Among four isolates of Myco. avium, three virulent ones induced a marked priming for TNF release and one avirulent strain did not. Mycobacterium tuberculosis H37Ra, which is very active in inducing TNF release due to its lipoarabinomannan moiety, was used to compare with the previous results. The growth of H37Ra in macrophages was increased in vitro by the neutralization of TNF and neutralization of either TNF and/or interferon-gamma (IFN-gamma) enhanced the in vivo proliferation of this microbe in the spleen and liver of infected animals, whereas only the combination of both anti-TNF and anti-IFN-gamma enhanced bacterial proliferation in the lung. We conclude that resistance to the avirulent strains of Myco. avium did not involve TNF, but rather antimicrobial mechanisms expressed constitutively in the mononuclear phagocytes. In contrast, TNF plays an important role in the control of Myco. tuberculosis H37Ra infection.

[Venous hemangioma of the mediastinum: apropos of a case]

A case of mediastinal venous hemangioma is reported. It's a benign tumor rarely found in the mediastinum. In the last six years, we only know three cases reported and none of them in our country. Clinical manifestations were cough and pleuritic pain. The diagnosis was suggested by radiologic examination and was confirmed by histologic study after thoracotomy. The mass was totally removed surgically and the evolution of the patient was favorable.

The relative impact of bacterial virulence and host genetic background on cytokine expression during Mycobacterium avium infection of mice

Resistance to Mycobacterium avium depends on both genetically encoded macrophage functions and acquired T-cell immunity. Cytokines may play a role in either type of resistance. We studied the expression of interleukin-2 (IL-2), IL-4 and interferon-gamma (IFN-gamma) in naturally susceptible BALB/c (Bcgs) and naturally resistant C.D2 (Bcgr) congenic mice infected with two strains of M. avium (one highly virulent and another of low virulence). We observed that cytokine expression patterns correlated better with the virulence of the micro-organism than with the genetic background of the host. The control of the infection by the low virulence strain in either mouse strain was associated with an increased expression of IFN-gamma and IL-2. Only Bcgs mice infected with a virulent strain of M. avium were unable to restrict bacterial growth. An increased expression of IL-4, early during infection, was detected in the course of the latter infection but played no role in determining the susceptibility to infection. Neutralization of IFN-gamma or IL-2 with specific monoclonal antibodies led to an exacerbation of the infection in Bcgr mice by the two strains of M. avium and in Bcgs mice infected with the low virulence strain of M. avium.

In vivo evidence for a non-T cell origin of interleukin-5

Eosinophil myelopoiesis is to a great extent regulated by interleukin (IL)-5. Analysis of IL-5 mRNA in spleen cell preparations by reverse transcription-polymerase chain reaction (RT-PCR) revealed the presence of message for this cytokine in uninfected severe combined immunodeficiency (SCID) mice. This message was increased following Mycobacterium avium infection. Normal BALB/c mice had higher levels of expression of IL-5 but the expression of this cytokine was reduced during M. avium infection. Anti-IL-5 monoclonal antibody administration in vivo to SCID mice reduced the number of peritoneal and splenic eosinophils. Gamma interferon (IFN-gamma) had an inhibitory effect of eosinophilopoiesis during infection of SCID mice by M. avium since neutralization of this cytokine increased the number of eosinophils detected in the peritoneal cavity of infected animals. Our results suggest that IL-5 may be produced by cells other than T cells that are both able to respond to infection and are under the control of IFN-gamma.

Characterization of the virulence of Mycobacterium avium complex (MAC) isolates in mice

The virulence of different isolates of MAC was studied in naturally susceptible BALB/c mice. In preliminary experiments, MAC bacteria forming smooth transparent colonies on solid media (SmT variants) were found to be virulent for BALB/c mice, causing progressive infection; smooth opaque (SmOp) were generally avirulent, being slowly eliminated from the infected organs; and rough (Rg) variants were either avirulent or as virulent as SmT variants. We chose to compare the virulence of different isolates of MAC of different origins, studying only the SmT morphotype. Strains of MAC isolated from naturally infected animals were those that most consistently caused progressive infections. AIDS patients-derived isolates were of intermediate virulence or devoid of virulence in mice. The environmental strains were eliminated from mice or did not proliferate. Strains of MAC isolated from individuals who were not infected by HIV varied in virulence from completely avirulent to highly virulent. There was no close correlation between virulence and restriction fragment length polymorphism (RFLP) type, although all highly virulent strains were of the A/I type. There was also no correlation between virulence analysed in vivo and the ability to grow in cultured macrophages.

Neutrophils as effector cells of T-cell-mediated, acquired immunity in murine listeriosis

The control of the infections caused by Listeria monocytogenes, considered an example of an intracellular parasite, is thought to involve co-operation between antigen-specific T cells and activated macrophages. Here we investigated the participation of polymorphonuclear leucocytes in the mechanisms of resistance during the immune phase of the antimicrobial response to L. monocytogenes infection. We found that BALB/c mice were unable to express T-cell-mediated (acquired) immunity to this pathogen in the absence of granulocytes. We propose that neutrophils should be included in the concept of cell-mediated immunity and that their antimicrobial role is not exclusively expressed during the early phases of a primary infection.

Role of gamma interferon and tumor necrosis factor alpha during T-cell-independent and -dependent phases of Mycobacterium avium infection

To design an effective immunotherapy for Mycobacterium avium infections, the protective host response to the infection must be known. Here we analyzed the role of gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) in the innate and acquired responses to M. avium infections in mice. T-cell depletion studies showed that CD4+ T cells were required for control of the infection. CD(4+)-depleted mice showed enhanced bacterial proliferation and at the same time showed a reduction in the level of expression of both IFN-gamma and TNF-alpha mRNAs in spleen cells. In contrast, M. bovis BCG immunization restricted M. avium proliferation and at the same time promoted expression of the mRNAs for the two cytokines. In vivo depletion studies using specific monoclonal antibodies showed that both IFN-gamma and TNF-alpha are involved in an early protection possibly involving NK cells, and furthermore, IFN-gamma is involved in the later T-cell-protective response to infection. In vivo neutralization of IFN-gamma during M. avium infection also blocked the priming for enhanced TNF-alpha secretion triggered by endotoxin. Both cytokines were found to be involved in the resistance expressed in BCG-immunized animals and exhibited additive bacteriostatic effects in vitro on bone marrow-derived macrophages infected with different strains of M. avium. These data suggest that both cytokines act in an additive or synergistic fashion in the induction of bacteriostasis and that IFN-gamma is also involved in priming TNF-alpha secretion.

Role of interleukin-6 in the induction of protective T cells during mycobacterial infections in mice

Interleukin-6 (IL-6) has been shown to regulate numerous functions of the immune system including the differentiation of T-cell subpopulations. Here we examined the involvement of this cytokine in the in vivo generation of a population of T cells able to protect mice against mycobacterial infections. BALB/c mice were infected intravenously with Mycobacterium avium 2447 and anti-IL-6 monoclonal antibodies were administered intraperitoneally throughout the course of the infection. Control mice were able to control the mycobacterial proliferation 1 month after inoculation, whereas mice whose IL-6 had been blocked showed progressive bacterial growth. To distinguish a role for IL-6 associated to the induction or expression of immunity mediated by T cells, we immunized mice with M. bovis bacillus Calmette-Guérin (BCG) Pasteur and challenged them 2 months later with M. avium. One group of mice received anti-IL-6 during the BCG vaccination and another during the M. avium challenge. When M. avium proliferation was assessed at day 30 of the challenge, it was found that the administration of anti-IL-6 during vaccination reduced the protection afforded by BCG compared to administration of the isotype control antibody. No difference in bacterial proliferation was observed at day 30 of challenge when antibodies were administered during M. avium challenge. Our results show that protective T cells arise during M. avium infections in mice after differentiating in the presence of IL-6.

Live but not heat-killed mycobacteria cause rapid chemotaxis of large numbers of eosinophils in vivo and are ingested by the attracted granulocytes

We studied leukocyte chemotaxis triggered by a local injection of mycobacteria (Mycobacterium avium and M. smegmatis) in BALB/c and C57BL/6 mice. Our experimental model consisted of the induction of a subcutaneous air pouch in the dorsal area of mice and inoculation 6 days later of 10(8) CFU of myocobacteria. Inflammatory exudates were harvested from the air pouch cavities 15, 30, and 45 min after the injection of the inocula. Injection of the microorganisms resulted in the migration of an elevated number of eosinophilic granulocytes into the inflammatory cavities. At 30 min after the inoculation of the mycobacteria, the air pouches contained between (3.9 +/- 0.3) x 10(5) (M. avium) and (3.3 +/- 0.3) x 10(5) (M. smegmatis) eosinophils, corresponding to more than one-third (41.4 to 38.3%) of the leukocytes present in the inflammatory cavities. Less than one-half of the eosinophils were attracted to the air pouches when the same number of heat-killed mycobacteria were inoculated [(1.3 +/- 0.2) x 10(5) cells for M. avium and (1.5 +/- 0.2) x 10(5) cells for M. smegmatis]. Injection of gram-negative bacteria (Escherichia coli), of latex beads, or of casein resulted in the attraction of inflammatory eosinophils in numbers that were comparable to those attracted by the heat-killed mycobacteria. Our data document the fact that live mycobacteria exert a rapid chemotactic effect on eosinophils. We therefore postulate that mycobacteria either contain or induce the production of an eosinophilotactic factor. Because this chemotactic effect occurs during the acute inflammatory response to mycobacteria, it cannot be due to the formation of immune complexes (a major infection-associated chemotactic factor for eosinophils). The attracted eosinophils had an important role in the local phagocytosis of mycobacteria, as indicated by our finding, derived from thin-section electron microscopy quantifications, that at 30 min after M. avium inoculation the inflammatory exudates contained (2.2 +/- 0.5) x 10(5) mycobacterium-bearing eosinophils (corresponding to 57% of the total eosinophils), as compared with (2.1 +/- 0.1) x 10(5) neutrophils and (1.5 +/- 0.2) x 10(5) macrophages with ingested bacilli. We conclude that mycobacteria induce the attraction of eosinophils to inflammatory sites and that these granulocytes have the capacity to phagocytize these bacilli in situ.