The primary immunodeficiencies

Acute lung pathology in the immunocompromised child

Children with compromised immune systems, whether due to primary or secondary immunodeficiencies, are susceptible to a broad spectrum of acute intrathoracic pathologies. These include infections, pulmonary edema, and malignancies. Pulmonary issues are common and perilous in this population, necessitating prompt and precise diagnosis for effective management. This review aims to provide an overview of such conditions, focusing on the imaging appearances of the most prevalent acute lung conditions affecting immunocompromised children. It emphasizes the critical importance of an integrated clinical and radiological approach when diagnosing these acute pulmonary disease states.

Immunodeficiency-Related Vaccine-Derived Poliovirus (iVDPV) Infections: A Review of Epidemiology and Progress in Detection and Management

Individuals with certain primary immunodeficiency disorders (PID) may be unable to clear poliovirus infection after exposure to oral poliovirus vaccine (OPV). Over time, vaccine-related strains can revert to immunodeficiency-associated vaccine-derived poliovirus (iVDPVs) that can cause paralysis in the patient and potentially spread in communities with low immunity. We reviewed the efforts for detection and management of PID patients with iVDPV infections and the epidemiology through an analysis of 184 cases reported to the World Health Organization (WHO) during 1962-2024 and a review of polio program and literature reports. Most iVDPV patients (79%) reported in the WHO Registry were residents in middle-income countries and almost half (48%) in the Eastern Mediterranean Region. Type 2 iVDPV was most frequently isolated (53%), but a sharp decline was observed after the switch to bivalent OPV in 2016, with only six cases reported during 2017-2024 compared to 63 during 2009-2016. Patients with common variable immunodeficiency have longer excretion of iVDPV than with other PID types. Implementation of sensitive sentinel surveillance to detect cases of iVDPV infection in high-risk countries and offer antiviral treatment to patients is challenged by competition with other health priorities and regulatory hurdles to the compassionate use of investigational antiviral drugs.

fSCIG 10% in pediatric primary immunodeficiency diseases: a European post-authorization safety study

BACKGROUND

The safety, tolerability, and immunogenicity of hyaluronidase-facilitated subcutaneous immunoglobulin (fSCIG) 10% (dual-vial unit of human immunoglobulin 10% and recombinant human hyaluronidase [rHuPH20]) were assessed in children with primary immunodeficiency diseases (PIDs).

METHODS

This phase 4, post-authorization, prospective, interventional, multicenter study (NCT03116347) conducted in the European Economic Area, enrolled patients aged 2 to < 18 years with a documented PID diagnosis who had received immunoglobulin therapy for ≥ 3 months before enrollment. New fSCIG 10% starters underwent fSCIG 10% dose ramp-up for ≤ 6 weeks (epoch 1) before receiving fSCIG 10% for ≤ 3 years (epoch 2); patients pretreated with fSCIG 10% entered epoch 2 directly. The primary outcome was the number and rate (per infusion) of all noninfectious treatment-related serious and severe adverse events (AEs).

RESULTS

In total, 42 patients were enrolled and dosed (median [range] age: 11.5 [3-17] years; 81% male; 23 new starters; 19 pretreated). Overall, 49 related noninfectious, treatment-emergent AEs (TEAEs) were reported in 15 patients; most were mild in severity (87.8%). No treatment-related serious TEAEs were reported. Two TEAEs (infusion site pain and emotional distress) were reported as severe and treatment-related in a single new fSCIG 10% starter. The rate of local TEAEs was lower in pretreated patients (0.1 event/patient-year) versus new starters (1.3 events/patient-year). No patients tested positive for binding anti-rHuPH20 antibodies (titer of ≥ 1:160).

CONCLUSIONS

No safety signals were identified, and the incidence of local AEs declined over the duration of fSCIG 10% treatment. This study supports fSCIG 10% long-term safety in children with PIDs. TRIAL REGISTRATION NUMBER (CLINICALTRIALS.GOV): NCT03116347.

Immunodeficiency is prevalent in congenital heart disease and associated with increased risk of emergency admissions and death

AIMS

To provide population-based data on the prevalence and clinical significance of immune deficiency syndromes (IDS) associated with congenital heart disease (CHD).

METHODS AND RESULTS

Utilizing administrative German Health System data the prevalence of increased susceptibility to infection (ISI) or confirmed IDS was assessed in CHD patients and compared with an age-matched non-congenital control group. Furthermore, the prognostic significance of IDS was assessed using all-cause mortality and freedom from emergency hospital admission. A total of 54 449 CHD patients were included. Of these 14 998 (27.5%) had ISI and 3034 (5.6%) had a documented IDS (compared with 2.9% of the age-matched general population). During an observation period of 394 289 patient-years, 3824 CHD patients died, and 31 017 patients experienced a combined event of all-cause mortality or emergency admission. On multivariable Cox proportional-hazard analysis, the presence of ISI [hazard ratio (HR): 2.14, P < 0.001] or documented IDS (HR: 1.77, P = 0.035) emerged as independent predictors of all-cause mortality. In addition, ISI and confirmed IDS were associated with a significantly higher risk of emergency hospital admission (P = 0.01 for both on competing risk analysis) during follow-up.

CONCLUSION

Limited immune competence is common in CHD patients and associated with an increased risk of morbidity and mortality. This highlights the need for structured IDS screening and collaboration with immunology specialists as immunodeficiency may be amenable to specific therapy. Furthermore, studies are required to assess whether IDS patients might benefit from intensified antibiotic shielding or tailored prophylaxis.

In-line warming reduces in-line pressure of subcutaneous infusion of concentrated immunoglobulins

Immunoglobulin replacement therapy is a life-saving treatment in patients with immunodeficiency and effective in the management of autoimmune disorders. Immunoglobulins are administered intravenously or subcutaneously, with the latter route reducing systemic reactions and providing an option for self-infusion, increasing patient convenience, while decreasing patient burden, healthcare utilization, and costs. A major limitation with subcutaneous administrations is the frequency of infusion due to limited volumes administrable into subcutaneous space, necessitating increased drug concentration, absorption, and dispersion. Increasing the concentration of immunoglobulins from 10 to 20% halves the required volume, but leads to higher dynamic viscosity, limiting infusion rate. Recombinant human hyaluronidase increases dispersion and absorption of immunoglobulins allowing administration of ≤ 600 mL per site, but does not change viscosity. Since the viscosity of fluids depends on temperature, we tested the feasibility of in-line warming of immunoglobulin formulations to physiological temperatures. In vitro analysis showed no negative impact of in-line warming to 38 °C on product quality. Subcutaneous infusion studies in pigs confirmed the feasibility of infusion rates of up to 7.5 mL/min with in-line warmed TAK-881, an immunoglobulin 20% facilitated with recombinant human hyaluronidase. In-line pressures were reduced compared with conventional immunoglobulin 20%, and local tolerance was not altered. Reduction of in-line pressures was more pronounced with thinner needle sets, indicating a potential benefit for patients. In summary, an in in-line warming device can circumvent the limitation of high viscosity, while product quality and local tolerance are maintained. The results of the presented studies warrant further testing in a phase 1 clinical study.

Bruton's tyrosine kinase regulates gut immune homeostasis through attenuating Th1 response

Inflammatory bowel disease (IBD) is driven by multiple genetic and environmental risk factors. Patients with mutations in Bruton’s tyrosine kinase (BTK) is known to manifest high prevalence of intestinal disorders including IBD. Although BTK mediates the signaling of various immune receptors, little is known how BTK maintains the homeostasis of the gut immune system. Here, we show that BTK-deficiency promotes IBD progression in a mouse model of colitis. Interestingly, the increased colitis susceptibility of BTK-deficient mice is not caused by gut microbiota changes but rather arises from enhanced pro-inflammatory Th1 response. More importantly, we find the heightened Th1 response in BTK-deficient mice to result from both T cell-extrinsic and -intrinsic mechanisms. BTK-deficient dendritic cells secret elevated levels of the Th1-polarizing cytokine IL-12 and BTK-deficient T cells are inherently more prone to Th1 differentiation. Thus, BTK plays critical roles in maintaining gut immune homeostasis and preventing inflammation via regulating T-cell polarization.

Fatal Progressive Meningoencephalitis Diagnosed in Two Members of a Family With X-Linked Agammaglobulinemia

Chronic enteroviral meningoencephalitis is a well-known complication in patients with X-linked agammaglobulinemia (XLA). However, progressive neurodegenerative disorders or chronic neuroinflammatory diseases with no causative microorganisms have been recognized as rare central nervous system (CNS) complications in XLA. We herein report a family in which two of three members with XLA had developed progressive meningoencephalitis with an unknown etiology. A 15-month-old male infant presented with left-sided ptosis. Initially, the family denied any family history of inherited diseases, but later disclosed a family history of agammaglobulinemia previously diagnosed in two family members. In the early 1980s, one of the elder brothers of the index patient's mother who had been treated with intramuscular immunoglobulin [or later intravenous immunoglobulin (IVIG)] for agammaglobulinemia deceased at 10 years of age after showing progressive neurological deterioration during the last several years of his life. The index patient was diagnosed with XLA caused by Bruton tyrosine kinase deficiency (654delG; Val219Leufs^*9), and chronic meningoencephalitis with an unknown infectious etiology. Magnetic resonance imaging of the brain demonstrated inflammatory changes in the basal ganglia, hypothalamus, midbrain, and pons, with multiple nodular lesions with ring enhancement, which showed impressive amelioration after the initiation of IVIG replacement therapy. Pleocytosis, which was characterized by an increase in CD4-positive and CD8-positive T cells expressing an activation marker and an elevation in inflammatory cytokines in the cerebrospinal fluid, was identified. No microorganism was identified as a cause of CNS complications. He thereafter developed brain infarction at 19 months of age and fatal status epilepticus at 5 years of age, despite regular IVIG with high trough levels and regular intraventricular immunoglobulin administration. The etiology of this rare CNS complication in XLA is currently unknown. Previous studies have suggested a possible association of IVIG, which was clearly denied in our index case because of the demonstration of his neurological disorder at presentation. In the future, extensive and unbiased molecular methods to detect causative microorganisms, as well as to investigate the possible role of autoimmunity are needed to clarify the etiology of CNS complications.

Mechanisms of Naturally Acquired Immunity to Streptococcus pneumoniae

In this review we give an update on the mechanisms of naturally acquired immunity against Streptococcus pneumoniae, one of the major human bacterial pathogens that is a common cause of pneumonia, septicaemia, and meningitis. A clear understanding of the natural mechanisms of immunity to S. pneumoniae is necessary to help define why the very young and elderly are at high risk of disease, and for devising new prevention strategies. Recent data has shown that nasopharynx colonization by S. pneumoniae induces antibody responses to protein and capsular antigens in both mice and humans, and also induces Th17 CD4+ cellular immune responses in mice and increases pre-existing responses in humans. These responses are protective, demonstrating that colonization is an immunizing event. We discuss the data from animal models and humans on the relative importance of naturally acquired antibody and Th17 cells on immunity to S. pneumoniae at three different anatomical sites of infection, the nasopharynx (the site of natural asymptomatic carriage), the lung (site of pneumonia), and the blood (site of sepsis). Mouse data suggest that CD4+ Th17 cells prevent both primary and secondary nasopharyngeal carriage with no role for antibody induced by previous colonization. In contrast, antibody is necessary for prevention of sepsis but CD4+ cellular responses are not. Protection against pneumonia requires a combination of both antibody and Th17 cells, in both cases targeting protein rather than capsular antigen. Proof of which immune component prevents human infection is less easily available, but two recent papers demonstrate that human IgG targeting S. pneumoniae protein antigens is highly protective against septicaemia. The role of CD4+ responses to prior nasopharyngeal colonization for protective immunity in humans is unclear. The evidence that there is significant naturally-acquired immunity to S. pneumoniae independent of anti-capsular polysaccharide has clinical implications for the detection of subjects at risk of S. pneumoniae infections, and the data showing the importance of protein antigens as targets for antibody and Th17 mediated immunity should aid the development of new vaccine strategies.

Are Janus Kinase Inhibitors Superior over Classic Biologic Agents in RA Patients?

The Janus Kinases (JAKs) are a family of intracellular tyrosine kinases that provide transmission signals from cytokine, interferons, and many hormones receptors to the nucleus resulting in synthesis of many biologically active compounds and changing cell metabolism and function. That was theoretical background to synthetize the JAK inhibitors (Jakinibs). In recent years a substantial battery of evidence has been collected indicating the potential role of Jakinibs to interact with the specific elements of the immune system, therefore changing the inflammatory response. JAK kinase blockade offers a unique opportunity to block most of the key cytokines enabling the deep interaction into immune system functioning. Following discovery first Jakinibs were intensively studied in various forms of autoimmune diseases, including rheumatoid arthritis, and finally two Jakinibs tofacitinib and Baricitinib have been approved for the treatment of rheumatoid arthritis. Some clinical data indicated that under special circumstances Jakinibs may be even superior to biologics in the treatment of RA; however this suggestion should be verified in large clinical and observational studies.

Emerging Infections and Pertinent Infections Related to Travel for Patients with Primary Immunodeficiencies

In today's global economy and affordable vacation travel, it is increasingly important that visitors to another country and their physician be familiar with emerging infections, infections unique to a specific geographic region, and risks related to the process of travel. This is never more important than for patients with primary immunodeficiency disorders (PIDD). A recent review addressing common causes of fever in travelers provides important information for the general population Thwaites and Day (N Engl J Med 376:548-560, 2017). This review covers critical infectious and management concerns specifically related to travel for patients with PIDD. This review will discuss the context of the changing landscape of infections, highlight specific infections of concern, and profile distinct infection phenotypes in patients who are immune compromised. The organization of this review will address the environment driving emerging infections and several concerns unique to patients with PIDD. The first section addresses general considerations, the second section profiles specific infections organized according to mechanism of transmission, and the third section focuses on unique phenotypes and unique susceptibilities in patients with PIDDs. This review does not address most parasitic diseases. Reference tables provide easily accessible information on a broader range of infections than is described in the text.

Primary Immunodeficiency Diseases in Highly Consanguineous Populations from Middle East and North Africa: Epidemiology, Diagnosis, and Care

Middle East and North Africa region (MENA)¹ populations are of different ethnic origins. Consanguineous marriages are common practice with an overall incidence ranging between 20 and 50%. Primary immunodeficiency diseases (PIDs) are a group of heterogeneous genetic disorders caused by defects in the immune system that predisposes patients to recurrent infections, autoimmune diseases, and malignancies. PIDs are more common in areas with high rates of consanguineous marriage since most have an autosomal recessive mode of inheritance. Studies of PIDs in the region had contributed into the discovery and the understanding of several novel immunodeficiency disorders. Few MENA countries have established national registries that helped in estimating the prevalence and defining common PID phenotypes. Available reports from those registries suggest a predominance of combined immunodeficiency disorders in comparison to antibody deficiencies seen in other populations. Access to a comprehensive clinical immunology management services is limited in most MENA countries. Few countries had established advanced clinical immunology service, capable to provide extensive genetic testing and stem cell transplantation for various immunodeficiency disorders. Newborn screening for PIDs is an essential need in this population considering the high incidence of illness and can be implemented and incorporated into existing newborn screening programs in some MENA countries. Increased awareness, subspecialty training in clinical immunology, and establishing collaborating research centers are necessary to improve patient care. In this review, we highlight some of the available epidemiological data, challenges in establishing diagnosis, and available therapy for PID patients in the region.

Salivary Immunoglobulins in Individuals with Common Variable Immunodeficiency

Oral manifestations of common variable immunodeficiency (CVID) are rare, have rarely been studied and have given controversial results. There are few data about IgA, IgG, and IgM antibody salivary levels in the literature, and there are few papers about the clinical impact of antibody deficiencies and CVID on the oral health of such patients. The aim of this study was to measure serum and salivary IgA, IgG, and IgM levels in CVID participants and controls, and to associate immunoglobulin levels with caries and periodontal disease. This was a case-control study involving 51 CVID individuals and 50 healthy controls. All participants underwent examination for dental caries and periodontal disease. Blood and whole saliva samples were collected on the same day of the oral examination. Serum IgA, IgM, and IgG levels were measured by turbidimetry and salivary IgA, IgM, and IgG titers were assessed by enzyme-linked immunosorbent assay. Incidences of caries and gingivitis were significantly higher in the CVID group than in the control group (p<0.05). Salivary and blood IgA and IgM titers were significantly reduced in the CVID group, but there was no association of salivary immunoglobulin levels with periodontal disease or with caries incidence (p>0.05 for both). Although CVID was associated with increased susceptibility to caries and gingivitis, it was not associated with low salivary levels of IgA and IgM.

Pattern recognitions receptors in immunodeficiency disorders

Pattern recognition receptors (PRRs) recognize common microbial or host-derived macromolecules and have important roles in early activation and response of the immune system. Initiation of the innate immune response starts with the recognition of microbial structures called pathogen associated molecular patterns (PAMPs). Recognition of PAMPs is performed by germline-encoded receptors expressed mainly on immune cells termed pattern recognition receptors (PRRs). Several classes of pattern recognition receptors (PRRs) are involved in the pathogenesis of diseases, including Toll-like receptors (TLRs), C-type lectin receptors (CLRs), and Nod-like receptors (NLRs). Patients with primary immune deficiencies (PIDs) affecting TLR signaling can elucidate the importance of these proteins in the human immune system. Defects in interleukin-1 receptor-associated kinase-4 and myeloid differentiation factor 88 (MyD88) lead to susceptibility to infections with bacteria, while mutations in nuclear factor-κB essential modulator (NEMO) and other downstream mediators generally induce broader susceptibility to bacteria, viruses, and fungi. In contrast, TLR3 signaling defects are associated with susceptibility to herpes simplex virus type 1 encephalitis. Other PIDs induce functional alterations of TLR signaling pathways, such as common variable immunodeficiency in which plasmacytoid dendritic cell defects enhance defective responses of B cells to shared TLR agonists. Altered TLR responses to TLR2 and 4 agonists are seen in chronic granulomatous disease (CGD) and X-linked agammaglobulinemia (XLA). Enhanced TLR responses, meanwhile, are seen for TLRs 5 and 9 in CGD, TLRs 4, 7/8, and 9 in XLA, TLRs 2 and 4 in hyper IgE syndrome (HIES), and for most TLRs in adenosine deaminase deficiency. In this review we provide the reader with an update on the role of TLRs and downstream signaling pathways in PID disorders.

Naturally Acquired Human Immunity to Pneumococcus Is Dependent on Antibody to Protein Antigens

Naturally acquired immunity against invasive pneumococcal disease (IPD) is thought to be dependent on anti-capsular antibody. However nasopharyngeal colonisation by Streptococcus pneumoniae also induces antibody to protein antigens that could be protective. We have used human intravenous immunoglobulin preparation (IVIG), representing natural IgG responses to S. pneumoniae, to identify the classes of antigens that are functionally relevant for immunity to IPD. IgG in IVIG recognised capsular antigen and multiple S. pneumoniae protein antigens, with highly conserved patterns between different geographical sources of pooled human IgG. Incubation of S. pneumoniae in IVIG resulted in IgG binding to the bacteria, formation of bacterial aggregates, and enhanced phagocytosis even for unencapsulated S. pneumoniae strains, demonstrating the capsule was unlikely to be the dominant protective antigen. IgG binding to S. pneumoniae incubated in IVIG was reduced after partial chemical or genetic removal of bacterial surface proteins, and increased against a Streptococcus mitis strain expressing the S. pneumoniae protein PspC. In contrast, depletion of type-specific capsular antibody from IVIG did not affect IgG binding, opsonophagocytosis, or protection by passive vaccination against IPD in murine models. These results demonstrate that naturally acquired protection against IPD largely depends on antibody to protein antigens rather than the capsule.

The identification of hematopoietic-specific regulatory elements for WASp gene expression

Chromosome Conformation Capture (3C) technology was used to identify physical interactions between the proximal Wiskott-Aldrich Syndrome protein (WASp) promoter and its distant DNA segments in Jurkat-T cells. We found that two hematopoietic specific DNase I hypersensitive (DHS) sites (proximal DHS-A, and distal DHS-B) which had high interaction frequencies with the proximal WASp promoter indicating potential regulatory activity for these DHS sites. Subsequently, we cloned several DNA fragments around the proximal DHS-A site into a luciferase reporter vector. Interestingly, no fragments showed enhancer activity, but two fragments exhibited strong silencing activity in Jurkat-T cells. After aligning the chromatin state profiling for hematopoietic and nonhematopoietic cells using the human genome browser (UCSC), we found a 5 kb putative hematopoietic specific enhancer region located 250 kb downstream of the WAS gene. This putative enhancer region contains two hematopoietic cell specific DHS sites. Subsequently, the hematopoietic specific DHS sites enhanced luciferase expression from the proximal WASp promoter in all hematopoietic cells we tested. Finally, using a lentiviral vector stable expression system, the hematopoietic specific-enhancer(s) increased GFP reporter gene expression in hematopoietic cells, and increased WASp gene expression in WASp deficient cells. This enhancer may have the potential to be used in gene therapy for hematological diseases.

Impact of rare diseases in oral health

Background

Rare diseases (RD) are those that present a lower prevalence than 5 cases per 10.000 population. The main objective of this review was to study the effect on oral health in rare diseases, while the secondary objective of the study is theme upgrade.

Material and Methods

Comparative observational case-control studies were analysed and a systematic review was conducted in PubMed. Each rare disease listed on the statistical data record of the Health Portal of the Ministry of Equality, Health and Social Policies Board of Andalusia was associated with “oral health”. The variables studied included dental, oral mucosa and occlusion alterations, oral pathologies (caries, periodontal disease) and other alterations (mouth breathing, parafunctional habits, etc). A bias analysis of the variable caries was conducted.

Results

Six RD were selected through our inclusion and exclusion criteria (hypogammaglobulinemia, Rett syndrome, Marfan syndrome, Prader-Willi syndrome, cystic fibrosis and Cri du chat syndrome) in a total of 8 publications, of which four trials were classified as high risk of bias and one of them as medium risk. There were not trials with low risk of bias.

Conclusions

The main statistically significant differences found by Syndrome compared to a control group were in Hypogammaglobulinemia with a greater tendency to enamel hypoplasia and dry mouth. The Rett syndrome had, as well, a greater tendency to an anterior open bite, ogival palate, bruxism, mouth breathing and tongue thrusting. Prader-Willi syndrome had a tendency of dental erosion, and Cri du chat syndrome showed a higher association to Tannerella forsythia.

Key words:Rare diseases, oral health.

Structure-Specific nuclease activities of Artemis and the Artemis: DNA-PKcs complex

Artemis is a vertebrate nuclease with both endo- and exonuclease activities that acts on a wide range of nucleic acid substrates. It is the main nuclease in the non-homologous DNA end-joining pathway (NHEJ). Not only is Artemis important for the repair of DNA double-strand breaks (DSBs) in NHEJ, it is essential in opening the DNA hairpin intermediates that are formed during V(D)J recombination. Thus, humans with Artemis deficiencies do not have T- or B-lymphocytes and are diagnosed with severe combined immunodeficiency (SCID). While Artemis is the only vertebrate nuclease capable of opening DNA hairpins, it has also been found to act on other DNA substrates that share common structural features. Here, we discuss the key structural features that all Artemis DNA substrates have in common, thus providing a basis for understanding how this structure-specific nuclease recognizes its DNA targets.

Btk Inhibitor RN983 Delivered by Dry Powder Nose-only Aerosol Inhalation Inhibits Bronchoconstriction and Pulmonary Inflammation in the Ovalbumin Allergic Mouse Model of Asthma

BACKGROUND

In allergen-induced asthma, activated mast cells start the lung inflammatory process with degranulation, cytokine synthesis, and mediator release. Bruton's tyrosine kinase (Btk) activity is required for the mast cell activation during IgE-mediated secretion.

METHODS

This study characterized a novel inhaled Btk inhibitor RN983 in vitro and in ovalbumin allergic mouse models of the early (EAR) and late (LAR) asthmatic response.

RESULTS

RN983 potently, selectively, and reversibly inhibited the Btk enzyme. RN983 displayed functional activities in human cell-based assays in multiple cell types, inhibiting IgG production in B-cells with an IC50 of 2.5 ± 0.7 nM and PGD2 production from mast cells with an IC50 of 8.3 ± 1.1 nM. RN983 displayed similar functional activities in the allergic mouse model of asthma when delivered as a dry powder aerosol by nose-only inhalation. RN983 was less potent at inhibiting bronchoconstriction (IC50(RN983) = 59 μg/kg) than the β-agonist salbutamol (IC50(salbutamol) = 15 μg/kg) in the mouse model of the EAR. RN983 was more potent at inhibiting the antigen induced increase in pulmonary inflammation (IC50(RN983) = <3 μg/kg) than the inhaled corticosteroid budesonide (IC50(budesonide) = 27 μg/kg) in the mouse model of the LAR.

CONCLUSIONS

Inhalation of aerosolized RN983 may be effective as a stand-alone asthma therapy or used in combination with inhaled steroids and β-agonists in severe asthmatics due to its potent inhibition of mast cell activation.

Association between common variable immunodeficiency and collagenous infiltrative disorders of the gastrointestinal tract: A series of four patients

Hypogammaglobulinemia/common variable immunodeficiency (CVID) may lead to disruption of the gut mucosal immune barrier. Collagenous infiltrative disorders of the intestinal tract (colitis, gastritis, sprue) constitute a relatively new spectrum of gastrointestinal disorders. Our aims were (1) to determine the association between immunoglobulin deficiency state like CVID and collagenous infiltrative disorders of the gut and (2) to study the clinic-pathologic characteristics and treatment outcomes in these patients. A retrospective search was conducted to identify cases with concurrence of these two conditions at an academic center from 2007 to 2013. Four such patients were identified from our database: three with collagenous colitis and one with collagenous gastritis. All patients with collagenous colitis had normal colonic mucosa while the patient with collagenous gastritis had nodular gastric mucosa. Only one patient out of four had decreased plasma cells in the submucosa as expected in low immunoglobulin states. All patients had improvement in their symptoms on immunoglobulin therapy with considerable remission on budesonide. Literature search revealed reporting of four similar patients. In conclusion, (1) the association between collagenous infiltrative disorders of the gut and CVID and its prompt response to immunoglobulins with effective maintenance with budesonide are novel findings. Our study also shows that the presence of plasma cells should not rule out the possibility of CVID. (2) In patients with chronic diarrhea, hypogammaglobulinemia and collagenous colitis/sprue should be considered for the available effective treatments such as immunoglobulins and budesonide.

BTK mutations selectively regulate BTK expression and upregulate monocyte XBP1 mRNA in XLA patients

Mutations in the Bruton agammaglobulinemia tyrosine kinase (BTK) gene are responsible for X-linked agammaglobulinemia (XLA). Unfolded or misfolded proteins can trigger stress pathways in the endoplasmic reticulum (ER), known as unfolded protein response (UPR). The aim was to clarify the involvement of UPR in XLA pathophysiology. By reverse transcription-quantitative PCR, we evaluated the expression of BTK and 12 UPR-related genes in eight patients. Moreover, we assessed the BTK protein expression and pattern in the patients' monocytes by flow cytometry and fluorescence immunocytochemistry. We found a reduced BTK expression in patients with stop codon mutations (P < 0.02). However, missense mutations did not affect BTK expression. Flow cytometry showed a reduction of BTK in patients which was corroborated by an absent or nonfunctional protein synthesis revealed by immunocytochemistry. In contrast with the other UPR-related genes, X-box binding protein 1 (XBP1) was markedly upregulated in the patients (P < 0.01), suggesting Toll-like receptor (TLR) activation since BTK directly interacts with TLRs as a negative regulator and XBP1 can be activated in direct response to TLR ligation. Different BTK mutations can be identified by the BTK expression. Inasmuch as UPR-related genes were downregulated or unaltered in patients, we speculate the involvement of the TLRs-XBP1 axis in the XLA pathophysiology. Such data could be the basis for further studies of this novel pathomechanism concerning XLA.

Comparative analysis of pathologic processes developing in mice housed in SPF vs non-SPF conditions and treated with cyclophosphamide and dsDNA preparation

In our earlier studies, we observed that when mice are treated with cyclophosphamide and fragmented exogenous dsDNA (18-30 h post cytostatic treatment), they develop a very characteristic set of symptoms and 80-90% of such animals succumb within 6-25 days. This was called "delayed death" phenomenon, and the gap between cyclophosphamide and DNA injections required for such phenotype to develop was termed "death window". We established that mice succumbed to multi-organ failure, which was caused by systemic inflammation and sepsis. These processes unfolded along with accidental involution of lymphoid organs, which resulted from the failure of CD34(+) hematopoietic stem cells to differentiate into lymphoid lineage progenitors. Here we compare SPF and non-SPF animals, and demonstrate that the major cause of systemic inflammation and sepsis observed upon such treatments is activation of an opportunistic infection. Mice of the same strain (CBA) housed under SPF conditions do not develop the characteristic symptoms, nor do they become moribund. Yet, regardless of the breeding conditions, upon synergistic action of cyclophosphamide and dsDNA, CD34(+) hematopoietic stem cells consistently fail to give rise to lymphoid lineage progenitors. We demonstrate that this differentiation defect is reversible and that population of lymphoid progenitors is restored by day 29 after cyclophosphamide injection.

Gene therapy studies in a canine model of X-linked severe combined immunodeficiency

Since the occurrence of T cell leukemias in the original human γ-retroviral gene therapy trials for X-linked severe combined immunodeficiency (XSCID), considerable effort has been devoted to developing safer vectors. This review summarizes gene therapy studies performed in a canine model of XSCID to evaluate the efficacy of γ-retroviral, lentiviral, and foamy viral vectors for treating XSCID and a novel method of vector delivery. These studies demonstrate that durable T cell reconstitution and thymopoiesis with no evidence of any serious adverse events and, in contrast to the human XSCID patients, sustained marking in myeloid cells and B cells with reconstitution of normal humoral immune function can be achieved for up to 5 years without any pretreatment conditioning. The presence of sustained levels of gene-marked T cells, B cells, and more importantly myeloid cells for almost 5 years is highly suggestive of transduction of either multipotent hematopoietic stem cells or very primitive committed progenitors.

Immunodeficiency and autoimmune enterocolopathy linked to NFAT5 haploinsufficiency

The link between autoimmune diseases and primary immunodeficiency syndromes has been increasingly appreciated. Immunologic evaluation of a young man with autoimmune enterocolopathy and unexplained infections revealed evidence of immunodeficiency, including IgG subclass deficiency, impaired Ag-induced lymphocyte proliferation, reduced cytokine production by CD8(+) T lymphocytes, and decreased numbers of NK cells. Genetic evaluation identified haploinsufficiency of NFAT5, a transcription factor regulating immune cell function and cellular adaptation to hyperosmotic stress, as a possible cause of this syndrome. Inhibition or deletion of NFAT5 in normal human and murine cells recapitulated several of the immune deficits identified in the patient. These results provide evidence of a primary immunodeficiency disorder associated with organ-specific autoimmunity linked to NFAT5 deficiency.

Screening for long-term poliovirus excretion among children with primary immunodeficiency disorders: preparation for the polio posteradication era in Bangladesh

BACKGROUND

Persons with primary immune deficiency disorders (PIDD) who receive oral poliovirus vaccine (OPV) may transmit immunodeficiency-associated vaccine-derived polioviruses (iVDPVs) and cause paralytic polio. The objective of this study was to identify children with PIDD in Bangladesh, and estimate the proportion with chronic poliovirus excretion.

METHODS

Patients admitted at 5 teaching hospitals were screened for PIDD according to standardized clinical case definitions. PIDD was confirmed by age-specific quantitative immunoglobulin levels. Stool specimens were collected from patients with confirmed PIDD.

RESULTS

From February 2011 through January 2013, approximately 96 000 children were screened, and 53 patients were identified who met the clinical case definition for PIDD. Thirteen patients (24%) had age-specific quantitative immunoglobulins results that confirmed PIDD. Of these, 9 (69%) received OPV 3-106 months before stool specimen collection. Among 11 patients, stool specimens from 1 patient tested positive for polioviruses 34 months after OPV ingestion. However, the poliovirus isolate was not available for genetic sequencing, and a subsequent stool specimen 45 days later was negative.

CONCLUSIONS

The risk of chronic poliovirus excretion among children with PIDD in Bangladesh seems to be low. The national polio eradication program should incorporate strategies for screening for poliovirus excretion among patients with PIDD.

Intravenous injection of a foamy virus vector to correct canine SCID-X1

Current approaches to hematopoietic stem cell (HSC) gene therapy involve the collection and ex vivo manipulation of HSCs, a process associated with loss of stem cell multipotency and engraftment potential. An alternative approach for correcting blood-related diseases is the direct intravenous administration of viral vectors, so-called in vivo gene therapy. In this study, we evaluated the safety and efficacy of in vivo gene therapy using a foamy virus vector for the correction of canine X-linked severe combined immunodeficiency (SCID-X1). In newborn SCID-X1 dogs, injection of a foamy virus vector expressing the human IL2RG gene resulted in an expansion of lymphocytes expressing the common γ chain and the development of CD3(+) T lymphocytes. CD3(+) cells expressed CD4 and CD8 coreceptors, underwent antigen receptor gene rearrangement, and demonstrated functional maturity in response to T-cell mitogens. Retroviral integration site analysis in 4 animals revealed a polyclonal pattern of integration in all dogs with evidence for dominant clones. These results demonstrate that a foamy virus vector can be administered with therapeutic benefit in the SCID-X1 dog, a clinically relevant preclinical model for in vivo gene therapy.

Characteristics of children with non-hodgkin lymphoma associated with primary immune deficiency diseases: descriptions of five patients

BACKGROUND

An increased incidence of non-Hodgkin lymphoma (NHL) has been seen in various primary immune deficiency (PID) cases. The present study aimed to evaluate the clinical characteristics and treatment outcomes of five cases with NHL associated with primary immunodeficiency.

METHODS

We retrospectively evaluated five patients with primary immunodeficiency who developed NHL. Two patients had ataxia-telangiectasia (A-T), one patient had common variable immunodeficiency (CVID), one patient had Bloom's Syndrome, and one patient had Wiskott-Aldrich syndrome (WAS).

RESULTS

All patients were male (median age, 8 years). Stage distribution was stage III in three patients and stage IV in two patients. Three patients had B-cell lymphoma and two had T-cell lymphoma. Reduced doses of Berlin-Frankfurt-Münster (BFM) and French Society of Pediatric Oncology (SFOP) regimens were used in four patients according to histopathological subtype. The two patients with ataxia and one patient with Bloom's Syndrome died of progressive/relapsed disease at months 5, 19, and 6, respectively. The patient with CVID associated with T-cell lymphoma has been in remission for 7 years. A full-dosage regimen of rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) was successfully used in the patient with WAS and B-cell lymphoma; he was still in remission after 3 years.

CONCLUSION

Primary immunodeficiency diseases are one of the strongest known risk factors for the development of NHL. Management of these patients remains problematic. There is a great need to develop new therapeutic approaches in this group. The use of rituximab in combination with CHOP may provide a promising treatment option for B-cell lymphomas associated with immunodeficiency.

Vav1 haploinsufficiency in a common variable immunodeficiency patient with defective T-cell function

Common variable immunodeficiency (CVID) is a primary immune disorder characterized by impaired antibody production, which is in many instances secondary to defective T cell function (T-CVID). We previously identified a subset of T-CVID patients characterized by defective expression of Vav1, a guanine nucleotide exchanger which couples the T-cell antigen receptor to reorganization of the actin cytoskeleton. Here we have addressed the possibility that an intrinsic defect in the Vav1 gene might underlie the reduction in Vav protein observed in T cells from these patients. We report the identification in one T-CVID patient of a heterozygous deletion in Vav1. The gene deletion, spanning exons 2-27, accounts for the reduction in Vav1 mRNA and protein in T cells from this patient. The disease-related pedigree of this patient suggests a de novo origin of the Vav1 deletion. The findings highlights Vav1 as an autosomal dominant disease gene associated with CVID with defective T-cell function.

Primary immunodeficiencies of pattern recognition receptors

Primary immunodeficiencies (PIDs) are severe defects in the capacity of the host to mount a proper immune response, and are characterized by an increased susceptibility to infections. Although classical immunodeficiencies have been characterized based on broad defects in cell populations (e.g. T/B cells or polymorphonuclear leukocytes) or humoral factors (e.g. antibodies or complement), specific immune defects based on well-defined molecular targets have been described more recently. Among these, genetic defects in pattern recognition receptors (PRRs), leading to impaired recognition of invading pathogens by the innate immune system, play an important role in specific defects against human pathogens. Defects have been described in three of the major families of PRRs: the Toll-like receptors, the C-type lectin receptors and the nucleotide-binding domain leucine-rich repeat-containing receptors. By contrast, no defects in the intracellular viral receptors of the RigI helicase family have been described to date. Defects in the PRRs show a broad variation in severity, have a narrow specificity for certain classes of pathogens, and often decrease in severity with age; these characteristics distinguish them from other forms of PIDs. Their discovery has led to important insights into the pathophysiology of infections, and may offer potential novel therapeutic targets for immunotherapy.

Host Defence against Bacterial Biofilms: “Mission Impossible”?

Bacteria living as biofilms have been recognised as the ultimate cause of persistent and destructive inflammatory processes. Biofilm formation is a well-organised, genetically-driven process, which is well characterised for numerous bacteria species. In contrast, the host response to bacterial biofilms is less well analysed, and there is the general believe that bacteria in biofilms escape recognition or eradication by the immune defence. In this review the host response to bacterial biofilms is discussed with particular focus on the role of neutrophils because these phagocytic cells are the first to infiltrate areas of bacterial infection, and because neutrophils are equipped with a wide arsenal of bactericidal and toxic entities. I come to the conclusion that bacterial biofilms are not inherently protected against the attack by neutrophils, but that control of biofilm formation is possible depending on a timely and sufficient host response.

Epigenetics, autoimmunity and hematologic malignancies: a comprehensive review

The relationships between immunological dysfunction, loss of tolerance and hematologic malignancies have been a focus of attention in attempts to understand the appearance of a higher degree of autoimmune disease and lymphoma in children with congenital immunodeficiency. Although multiple hypotheses have been offered, it is clear that stochastic processes play an important role in the immunopathology of these issues. In particular, accumulating evidence is defining a role of epigenetic mechanisms as being critical in this continuous spectrum between autoimmunity and lymphoma. In this review, we focus attention predominantly on the relationships between T helper 17 (Th17) and T regulatory populations that alter local microenvironments and ultimately the expression or transcription factors involved in cell activation and differentiation. Abnormal expression in any of the molecules involved in Th17 and/or Treg development alter immune homeostasis and in genetically susceptible hosts may lead to the appearance of autoimmunity and/or lymphoma. These observations have clinical significance in explaining the discordance of autoimmunity in identical twins. They are also particularly important in the relationships between primary immune deficiency syndromes, immune dysregulation and an increased risk of lymphoma. Indeed, defining the factors that determine epigenetic alterations and their relationships to immune homeostasis will be a challenge greater or even equal to the human genome project.

Necrotizing periodontitis as a possible manifestation of common variable immunodeficiency

Common variable immunodeficiency (CVID) is an inherited disease characterized by hypogammaglobulinaemia and impaired humoural immunoresponse and is mainly associated with recurrent infections of the airway and the digestive tract. An 18-year old female with a diagnosis of CVID associated with a devastating necrotizing periodontitis, ultimately resulting in complete destruction of the periodontium and loss of all teeth, is reported. Clinical, biochemical, microbiological and radiographic examinations are presented. The report highlights the likely importance of immunoglobulin replacement and intensive dental hygiene in CVID patients, and the devastating effect of non-compliance in such patients.

Prevalence of primary immunodeficiency in Korea

This study represents the first epidemiological study based on the national registry of primary immunodeficiencies (PID) in Korea. Patient data were collected from 23 major hospitals. A total of 152 patients with PID (under 19 yr of age), who were observed from 2001 to 2005, have been entered in this registry. The period prevalence of PID in Korea in 2005 is 11.25 per million children. The following frequencies were found: antibody deficiencies, 53.3% (n = 81), phagocytic disorders, 28.9% (n = 44); combined immunodeficiencies, 13.2% (n = 20); and T cell deficiencies, 4.6% (n = 7). Congenital agammaglobulinemia (n = 21) and selective IgA deficiency (n = 21) were the most frequently reported antibody deficiency. Other reported deficiencies were common variable immunodeficiencies (n = 16), X-linked agammaglobulinemia (n = 15), IgG subclass deficiency (n = 4). Phagocytic disorder was mostly chronic granulomatous disease. A small number of patients with Wiskott-Aldrich syndrome, hyper-IgE syndrome, and severe combined immunodeficiency were also registered. Overall, the most common first manifestation was pneumonia. This study provides data that permit a more accurate estimation PID patients in Korea.

The feasibility of identifying children with primary immunodeficiency disorders: preparation for the polio post-eradication era in Bangladesh

BACKGROUND

Persons with primary immunodeficiency disorders (PIDD) who receive oral poliovirus vaccine (OPV) or are household contacts of OPV recipients are at risk of excreting immunodeficiency-associated vaccine-derived polioviruses (iVDPVs). iVDPVs can be transmitted and cause paralytic polio. The objective of this study was to determine the feasibility of identifying infants and young children with PIDD in Bangladesh, and among those identified, to estimate the proportion excreting iVDPVs.

METHODS

Patients admitted at 5 referral and teaching hospitals from the hospital catchment area were screened for PIDD using a standardized clinical case definition. PIDD was confirmed using results of testing for age-specific quantitative immunoglobulins (QIGs) levels. Stool specimens were collected according to WHO guidelines from children with confirmed PIDD.

RESULTS

During February-July 2009, 13 patients were identified who met the clinical case definition for PIDD; their median age was 1.4 years (range: 2 months to 10 years). Six (46%) of the patients had age-specific QIG results that confirmed PIDD. Stool specimens from four patients tested negative for polio vaccine viruses. All four had received OPV between 50 and 264 days prior to study recruitment.

CONCLUSION

Identifying children with PIDD at referral and teaching hospitals in Bangladesh is feasible, but a larger number of patients is needed to estimate the risk for iVDPV excretion. The national polio eradication program should expand surveillance for PIDD case-patients and regularly test persons with PIDD for poliovirus excretion. These efforts will be essential for developing effective prevention and control strategies following OPV cessation, especially for densely populated and tropical countries like Bangladesh where even a minimal iVDPV risk could have significant public health consequences.

Oral manifestations in patients with hypogammaglobulinemia

OBJECTIVE

The overall objective of this study was to assess the oral manifestations and their association with immunologic status and health history, of individuals with hypogammaglobulinemia.

STUDY DESIGN

A case-controlled study of 100 subjects with hypogammaglobulinemia and 93 control individuals was performed. All participants were examined for dental caries, periodontal disease, mucosal lesions/infections, and general oral health problems. Decayed, missing, filled teeth and community periodontal index were recorded. Complete blood count, serum immunoglobulins, and lymphocyte immunophenotyping were measured on the same day of the oral health assessment.

RESULTS

Individuals with hypogammaglobulinemia showed higher prevalence of enamel hypoplasia and complaints of dry mouth, and lower prevalence of dental caries and periodontal disease.

CONCLUSIONS

The systemic conditions associated with hypogammaglobulinemia were not associated with enhanced susceptibility to caries, gingivitis, or periodontitis; however, individuals with hypogammaglobulinemia were more likely to report more episodes of recurrent aphthous ulcers compared with control individuals.

Pandemic influenza vaccination elicits influenza-specific CD4+ Th1-cell responses in hypogammaglobulinaemic patients: four case reports

In these case reports, we investigated pandemic influenza 2009 vaccination of primary hypogammaglobulinaemic patients. Three combined variable immunodeficiency (CVID) patients and one X-linked agammaglobulinaemia (XLA) patient were vaccinated with the pandemic vaccine A/California/7/2009 (H1N1)-like split virus (X179a) adjuvanted with the oil-in-water emulsion AS03. Subsequently, serum and peripheral blood mononuclear cells were sampled and used to measure the haemagglutination inhibition (HI) and antibody-secreting cell (ASC) responses. In addition, the IFN-γ, IL-2 and TNF-α producing CD4(+) Th1-cell response was determined as these cytokines are important indicators of cell-mediated immunity. Two of the CVID patients responded to vaccination as determined by a >4-fold rise in HI antibodies. These subjects also had influenza-specific ASC numbers, which, albeit low, were higher than prevaccination levels. In addition, vaccination induced CD4(+) Th1-cell responses in both the XLA patient and the CVID patients, although the frequency of influenza-responsive cells varied amongst the patients. These results suggest that hypogammaglobulinaemia patients can mount a CD4(+) Th1 cell-mediated response to influenza vaccination and, additionally, that influenza vaccination of some hypogammaglobulinaemia patients can produce an influenza-specific humoral immune response. The findings should be confirmed in larger clinical studies.

A novel immunodeficiency disorder characterized by genetic amplification of interleukin 25

Many primary immunodeficiency disorders of differing etiologies have been well characterized, and much understanding of immunological processes has been gained by investigating the mechanisms of disease. Here, we have used a whole-genome approach, employing single-nucleotide polymorphism and gene expression microarrays, to provide insight into the molecular etiology of a novel immunodeficiency disorder. Using DNA copy number profiling, we define a hyperploid region on 14q11.2 in the immunodeficiency case associated with the interleukin (IL)-25 locus. This alteration was associated with significantly heightened expression of IL25 following T-cell activation. An associated dominant type 2 helper T cell bias in the immunodeficiency case provides a mechanistic explanation for recurrence of infections by pathogens met by Th1-driven responses. Furthermore, this highlights the capacity of IL25 to alter normal human immune responses.

Ex vivo γ-retroviral gene therapy of dogs with X-linked severe combined immunodeficiency and the development of a thymic T cell lymphoma

We have previously shown that in vivo γ-retroviral gene therapy of dogs with X-linked severe combined immunodeficiency (XSCID) results in sustained T cell reconstitution and sustained marking in myeloid and B cells for up to 4 years with no evidence of any serious adverse effects. The purpose of this study was to determine whether ex vivo γ-retroviral gene therapy of XSCID dogs results in a similar outcome. Eight of 12 XSCID dogs treated with an average of dose of 5.8 × 10(6) transduced CD34(+) cells/kg successfully engrafted producing normal numbers of gene-corrected CD45RA(+) (naïve) T cells. However, this was followed by a steady decrease in CD45RA(+) T cells, T cell diversity, and thymic output as measured by T cell receptor excision circles (TRECs) resulting in a T cell lymphopenia. None of the dogs survived past 11 months post treatment. At necropsy, few gene-corrected thymocytes were observed correlating with the TREC levels and one of the dogs was diagnosed with a thymic T cell lymphoma that was attributed to the gene therapy. This study highlights the outcome differences between the ex vivo and in vivo approach to γ-retroviral gene therapy and is the first to document a serious adverse event following gene therapy in a canine model of a human genetic disease.

Pulmonary complications in patients with antibody deficiency

OBJECTIVE

The aim of this study was to evaluate pulmonary complications in patients with primary antibody deficiency (X-linked agammaglobulinaemia [XLA] and common variable immunodeficiency [CVID]).

METHODS

Thirty patients over six years of age regularly followed in a reference out-patient clinic on primary immunodeficiency were studied. All of them have been treated with intravenous immunoglobulin (IVIG) replacement therapy. Pulmonary complications were evaluated analysing clinical data (medical records review), lung function test (spirometry) and pulmonary imaging (chest computed tomography [CCT]).

RESULTS

Patients with normal CCT (N = 14) and those with abnormal CCT (N = 16) have shown no differences regarding the age at onset of symptoms, age of diagnosis, and duration of IVIG treatment. The mean number of pneumonia episodes before IVIG replacement was significantly higher among patients with abnormal CCT (4 vs 7 episodes, p = 0.008). CCT abnormalities observed in 16 patients were: bronchiectasis (12/16); peribronchial thickening (3/16); air trapping (5/16); lung volume reduction (4/16); atelectasis (2/16), follicular bronchiolitis and ground-glass abnormality (2/16) and parenchyma nodule (1/16). Lung function tests showed ventilatory disturbance in 18/30: obstructive pattern in 38.8%, restrictive pattern in 44.4%, and mix pattern in 16.7%. There were no significant differences in lung function between those with and without CCT abnormalities. Negative significant correlations were observed between lung function and number of episodes of pneumonia. Chronic persistent cough was associated with a reduction in lung function.

CONCLUSIONS

Pulmonary complications are not rare in patients with antibody deficiencies and they must be monitored.

Defects of pattern recognition: primary immunodeficiencies of the innate immune system

Genetic defects leading to impaired recognition of invading pathogens by the innate immune system, and hence to increased susceptibility to specific classes of microorganisms have been recently recognized. To date, defects have been described in three of the major families of pattern recognition receptors (PRRs): the Toll-like receptors (TLRs), the C-type lectin receptors (CLRs), and the nucleotide binding domain leucine-rich repeat containing receptors (NLRs). By contrast, defects in the viral receptors RigI helicases have not been found. PRR defects vary greatly in severity, display a narrow susceptibility profile towards specific pathogens, and when severe in infancy and childhood, often decrease in severity thereafter. Their discovery leads to crucial insight in the pathophysiology of infections, and offer therapeutic targets for future immunotherapy.

Pulmonary infections

This paper reviews the most common imaging findings of pulmonary infection in children. Pneumonia is a leading cause of mortality in children in developing and industrialized countries. While the imaging findings usually are nonspecific, correlation with the patient's age, immune status and pertinent history can limit the differential diagnoses. The paper will review the common and unique features of pneumonia caused by specific organisms and in specific patient populations.