Bibliographic Updates in Allergy

30.01.2009
Bibliographic Updates in Allergy

October 2008
Claude MOLINA and Franz MARRACHE

  • «Inflammometry» in the treatment of Asthma
  • Determining factors for pet ownership: their relationship with Asthma & Allergy
  • Allergists face to Primary Immune Deficiencies (PID)
  • Genetic approach to Primary Immune Deficiencies
  • Genetics, Asthma, and Passive Smoking

« Inflammometry » in the treatment of Asthma
Bronchial inflammation is, with more or less variable obstruction, one of the components of asthma. Its assessment entitled « Inflammometry » (I.D. Pavord et al. Lancet 2008; 372: 1017-1018) cannot be performed either clinically, apart from exacerbation periods, or by spirometry even when associated with multiple daily peak flow recordings. Thus, these authors tried to found eosinophils in spontaneous or induced sputum as well as to measure the fraction of nitric oxide (NO) in exhaled air (FE NO) which is currently facilitated by practical and cheap monitoring devices. Association of these 2 techniques allow ascertaining indication for therapy as well as appreciating the efficacy of anti-inflammatory treatment with corticoïds. Indeed, the authors acknowledge that induced sputum is a demanding technique and cannot always be easily performed in asthmatic patients whose expectoration is often scarce.
In addition, even if FE NO concentration (between 25 and 50 ppm) correlates well with the presence of eosinophils and justifies the indication for and maintenance of corticotherapy, its validity is far from being unanimous. Thus, S.J. Szefler et al (Management of Asthma based on exhaled nitric oxide in addition to guideline-based treatment for inner city adolescents and young adults : a randomised controlled trial : Lancet 2008; 372: 1065-1072)think it   does not bring any benefit and rather may induce an unwarranted increase of inhaled corticosteroid doses.
Similarly, de De Jongste et al (Daily telemonitoring of exhaled NO and symptoms in the treatment of chilhood asthma. Am. J. Respir. Crit. Care Med.  17 October 2008) note that a sophisticated equipment do not have any advantage over the standard technique.

In conclusion in the treatment and monitoring of asthma, the assessment of airway inflammation is an interesting complement to clinical aspects and lung function testing. However, the former cannot replace the latter and vice-versa.
Determining factors for pet ownership : their relationship with Asthma and Allergy
It is known that the presence of a pet (cats and dogs, in particular) is regarded by some authors as a risk factor for asthma and allergy, whereas others assign them a protective role. Such divergence of opinion might be due to a wrong interpretation in epidemiologic studies which do not take into account all confounding factors.

This highlights the interest of this meta-analysis of factors determining ownership of a cat or a dog. This study involved the monitoring of 12 European cohorts from 7 different countries, each one including between 485 and 4089 allergic (rhinitis, eczema) or asthmatic children, for a total of 25056 families.
Questionnaires used included questions on previous history of allergies and Asthma in the children and their parents, parental educational level, the number of children in the family, access to residence (ground floor) the presence of one or many pets (E. Eller et al. Meta-analysis of determinants for pet ownership in 12 European birth cohorts on asthma and allergies: A GA²LEN initiative.  Allergy 2008; 63: 1491-1498).

In this study, 14.9% of the families had at least one cat, and 12% at least one dog. A family history of allergy significantly decreased the opportunity of owning a cat (OR 0.91; CI 95% 0.85-0.99) or a dog (OR 0.90 ; 0.86-0.94).
A high level of parental education also decreased such opportunity, which was more evident for cats than for dogs.
Apart from this, the older the children are, the lower the chances are for a family to own a cat. That was not seen in the case of dogs.
Finally, the convenience of ground access is a factor which favours owning a pet, whereas the number of children is not associated with its presence.

Thus, socio-demographic factors such as family history of allergy, a high parental educational level, home ground access, must be taken into consideration in all european statistical study that may wish to analyse the influence of pets on allergy or asthma in children.
Allergists face to Primary Immune Deficiencies (PID)
PID  include approximately150 identified diseases, 120 of which are due to genetic defects. They are relatively rare, and their diagnosis depends upon the sagacity of the doctor and the laboratory support in the area or region concerned.
This highlights the interest of the general review dedicated to « Common variable immunodeficiency » by English-speaking authors (M. A. Park et al.  Lancet 2008: 372 ; 489-502) corresponding to Hypo- or Agammaglobulinemia or Humoral PID of the French litterature. It represents 65% of PID and  is characterised by repetitive bouts of sinus and pulmonary infections, affecting the young adult, male or female, and in whom one detects a clear decrease of serum levels of at least two immunoglobulins: IgA , IgG or IgM.
The allergist or pulmonologist may therefore have to face these patients with upper (sinusitis) or lower (pneumonia) airway infections which mimic asthma or chronic bronchitis, and which are due to Hemophilus influenzae or Mycoplasma and may  justify antibiotics in primary care .
However, the association with other symptoms may draws  attention :
Auto-immune manifestations : thrombocytopenic purpura or haemolytic anemia, Pulmonary complications such as bronchectasis or granulomatosis resembling sarcoidosis, or Gastro-intestinal problems similar to Crohn’s disease or coeliac disease, or Non-hodgkin Lymphoma.

The diagnosis comprises 3 steps :
1st step : F.B.C. (Full blood count) and determination of serum Immunoglobulins, as well as search for proteins in the urine (to exclude a nephrotic syndrome)
2nd step : Determination of serum levels of IgG sub-classes (IgG1 to IgG 4), anti-diphteria and anti-tetanus antibodies and haemagglutinins as well as an antibody response to Streptococcus Pneumoniae type polysaccharide vaccination.
In fact, the absence of antibodies requires replacement treatment with intravenous or sub-cutaneous  Immunoglobulins, as suggested by M.L. Moore and J.M. Quinn (Annals of Allergy 2008; 101: 114-121).
It is also relevant at this stage to quantify, by flow cytometry, B and T Lymphocytes as well as Natural Killer cells, whereas the study of B sub-populations will be part of the 3rd step.
3rd step : essentially genetic studies (which will be discussed next)

Genetic approach to Primary Immune Deficiencies
In the case of PID described beforehand, genetic studies are rarely indicated since corresponding mutations are rare and not always clinically relevant. In 15% of the cases, particularly when Agammaglobulinemia is associated with an absence or a very low percentage of B Lymphocytes, involved genes have been described : ICOS (Inducible T cell Costimulator) in 9 patients, TNF superfamily : 13 B in 17 patients and 13 C in one patient, and CD19 in 4 patients. As for the other PID, mainly seen in infants and children, their prognosis is often severe, and they present with different clinical phenotypes.
When a phagocytic deficit or a chronic septic granulomatosis are suspected, one should do a neutrophil count, study their chemotactic response and their phagocytic capacity using a Nitro-Blue Tetrazolium or a Dihydro-Rhodamine stain and flow cytometry for detection of expression of CD11/CD18 before studying the gene.
When one suspects that cell Immunity is affected, analysis should initially include a flow cytometry study of the percentage of T lymphocytes, and Natural Killer cell subpopulations as well as an in vivo and in vitro analysis of T cell function.

Several detailed tables of the most frequent PID and implicated genes are published in the paper by H.K. Lehman et al (The use of commercially available genetic tests in immunodeficiency disorders.  Ann. Allergy Asthma Immunol. 2008; 212-218) and include the addresses of Laboratories specializing in the study of these diseases in the US.

Such genetic studies must be performed after having obtained a written informed consent from the patients and/or their families. They are carried out in the blood or in oral scrapings, particularly in severely leucopenic patients (in whom the amount of necessary DNA may be insufficient in the blood) or in the case where a bone marrow transfer must be performed (which may contain donor blood cells).

In France, it is mainly at Hôpital Necker, in Paris, that after the internationally acknowledged contribution by C. Nezelof, the remarkable work by Alain Fischer on SCID (Severe Combined Immune Deficiencies, which are most often X-linked and potentially lethal) has applied gene therapy which has proven to be very efficacious, thanks to the introduction of genes using retroviral vectors(Thérapie  génique des Déficits immunitaires Sévères. A. Fischer et al. Bull.Acad. Nat. Med. 2005; 189: 779-788)

Genetics , Asthma, and Passive Smoking
In a study involving the human genome, a group of French researchers had shown the association between certain genetic variations in chromosome 17q21 and an increased risk of Asthma.
In order to elucidate this association, a larger study was performed involving various clinical phenotypes of the disease (Effect of 17q21 variants and smoking exposure in early onset asthma. E. Bouzigon et al.  N. Eng. J. Med. 2008 359 19 November 6 1985-1994 ).

The methodology involved testing for 36 SNP (single nucleotide polymorphism) in the 17q21 region in 1511 asthmatic patients from 372 families. The age at onset of asthma and early passive exposure to tobacco smoke (from parents) were also taken into consideration.

11 SNP were significantly associated with Asthma, of which 3 were very strongly and 4 were strongly associated with an early-onset asthma (4 years old or younger). By contrast, no association was observed with late-onset asthma.

Furthermore, a very strong association was seen between 6 SNP and early-onset asthma when the children had been early exposed, to passive smoking. A specific genetic variant (re8069176)  was associated with a 3-fold higher risk of asthma than other genotypes.

Therefore this excellent study shows the joint effect of genetic (chromosome 17q21, in this case) and environmental factors (here tobacco-smoke) upon the pathophysiology of asthma, in the context of passive smoking by the young child.
Source: CEFCAP

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