Endokrynologia PediatrycznaPediatric Endocrinology

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Vol. 10/2011 Nr 4(37)

Endokrynologia Pediatryczna Pediatric Endocrinology

ABSTRACT/STRESZCZENIE

Aims. Chlamydia pneumoniae (CP) is one of the most common human pathogens. The course of the infection is related to the immunological condition of the patient. CP is capable of staying long and multiplying in infected cells.

Infection with CP is more and more often associated with diseases of noninfectious etiology. The study is an attempt to answer the question if infection with CP can be related to type1 diabetes in children. Methods. The study comprised 47 children with type 1 diabetes. The control group consisted of 37 children hospitalized due to suspected anatomical and/or functional deviations in the urinary system. Diabetic children were divided into two subgroups: 23 children with the recent onset diabetes and 24 children with the disease present for 3 to 8 years (long-lasting diabetes). The serum level of IgM and IgG antibodies to CP was determined with the use of the immunoenzymatic ELISA test. Sha- piro–Wilk test was used for statistical analysis of distribution of the studied variables. The significance of differences was assessed with Mann–Whitney test. Results. In the whole group of children with diabetes and in group with the recent onset diabetes the serum level of IgM antibodies to CP was significantly higher than in the control group while the difference between the level of IgG remained insignificant. In the group of children with the recent onset diabetes IgM antibodies were significantly higher than IgG. In the group with long lasting diabetes IgG antibodies were higher than in the control group but the difference was considered close to significance. The IgM level in the two groups did not differ significantly. Conclusions. The significantly higher serum level of IgM antibodies to CP in the group with the recent onset type 1 diabetes compared to the control group as well as the significantly higher level of IgM antibodies than IgG found in this group may indicate a correlation between the CP infection and type 1 diabetes. Pediatr.

Endocrinol. 10/2011;4(37):19-26.

Wstęp. Chlamydia pneumoniae (CP) należy do najbardziej rozpowszechnionych patogenów ludzkich. Przebieg in- fekcji przez niego wywołanej zależy od stanu układu immunologicznego pacjenta. CP ma zdolność do długotrwałego utrzymywania się i namnażania w zakażonych komórkach. Zakażenie CP coraz częściej wiązane jest z chorobami o etiologii niezakaźnej. Praca jest próbą odpowiedzi na pytanie, czy istnieje związek między zakażeniem CP a cukrzycą

Chlamydia Pneumoniae Infection in Children with Type 1 Diabetes Mellitus Zakażenie Chlamydia Pneumoniae u dzieci z cukrzycą typu 1

1

Bożena Banecka,

²

Beata Bieniaś,

¹

Leszek Szewczyk

1Department of Pediatric Endocrinology and Diabetology, Medical University, Lublin, Poland

2Department of Pediatric Nephrology, Medical University, Lublin, Poland

Corresponding autor: Bożena Banecka, Department of Pediatric Endocrinology and Diabetology, Medical University of Lublin, ul. Chodźki 2, 20-096 Lublin, Poland, e-mail:baneckab@tlen.pl

Keywords: Chlamydia pneumoniae, type1 diabetes in children Słowa kluczowe: Chlamydia pneumoniae, cukrzyca typu 1 u dzieci

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typu 1 u dzieci. Materiał i metody. Badaniem objęto 47 dzieci chorujących na cukrzycę typu 1. Grupę kontrolną sta- nowiło 37 dzieci hospitalizowanych z powodu podejrzenia odchyleń anatomicznych i/lub czynnościowych w ukła- dzie moczowym. Dzieci chore na cukrzycę podzielono na dwie podgrupy: 23 dzieci ze świeżym zachorowaniem na cukrzycę oraz 24 dzieci z czasem trwania cukrzycy od 3 do 8 lat. Dokonano oznaczenia poziomu przeciwciał przeciw CP w klasie IgG i IgM za pomocą immunoenzymatycznego testu ELISA. Do analizy statystycznej rozkładu badanych zmiennych użyto testu Shapiro–Wilka. Istotność różnic między grupami oceniono testem Manna–Whitneya dla rozkładu nieparametrycznego. Wyniki. Poziom przeciwciał przeciw CP w klasie IgM był istotnie wyższy w gru- pie wszystkich dzieci chorych na cukrzycę w porównaniu z grupą kontrolną, natomiast różnica poziomu przeciwciał w klasie IgG między tymi grupami była statystycznie nieistotna. W grupie ze świeżym zachorowaniem na cukrzycę poziom p/c IgM był istotnie wyższy niż poziom IgG. W grupie z długim czasem trwania cukrzycy poziom p/c IgG był wyższy niż w grupie kontrolnej, ale ta różnica była jedynie bliska istotności. Różnica poziomu p/c IgM między tymi grupami nie była istotna. Wnioski. Istotnie wyższy poziom p/c IgM przeciw CP w grupie ze świeżym zachorowaniem na cukrzycę w porównaniu z grupą kontrolną oraz istotnie wyższy poziom p/c IgM niż IgG w tej grupie może wska- zywać na związek między zakażeniem CP a cukrzycą typu 1. Endokrynol. Ped. 10/2011;4(37):19-26.

they can also inhibit activation of complement in an alternative way, thus delaying a non-specific immune response [10, 11]. CP is also capable of pro- ducing heat shock proteins, which may lead to the phenomenon of antigenic mimicry with human proteins [12]. Infection with CP is more and more often associated with diseases of noninfectious etiology:

bronchial asthma, arteriosclerosis, obesity, arthritis, erythema nodosum, neoplasms, iritis, mediastinum adenitis, myocarditis, hepatitis, cerebral palsy, mul- tiple sclerosis, Alzheimer’s disease, neuroinfections [4, 8, 13–28].

Recently, it has been reported that there is a relationship between infection with CP and the development of diabetic nephropathy, diabetic cardiovascular disease and diabetic erectile dysfunction [29–31].

The study is an attempt to answer the question if infection with CP can be related to type 1 diabetes in children.

Materials and methods

The study comprised 47 children with type 1 diabetes. The control group (C) consisted of 37 children hospitalized due to suspected anatomical and/or functional deviations in the urinary system. The age of the patients ranged between 2 and 18 years.

Diabetic children were divided into two subgroups:

group R comprising 23 children with the recent onset diabetes and group L – 24 children with the disease present for 3 to 8 years (long-lasting diabetes). The level of antibodies against CP in the IgG and IgM class was determined with the use of the immunoenzymatic ELISA test in both diabetic and control group children. Shapiro–Wilk test was used for statistical analysis of distribution of the studied

Introduction

Chlamydia pneumoniae (CP) is a Gram-nega- tive, coccoid bacterium belonging to the most common human pathogens. It has biological properties of both bacteria and viruses. Due to the incapability of synthesizing its own ATP, the development of CP is possible only within a host cell [1–3]. Bacteria enter the lungs, multiply in mononuclear leukocytes and are carried with blood to different sites in the organism infecting many types of host cells (e.g.

tissue macrophages, smooth muscle cells in ves- sels, endothelial cells) [3–5]. The infection may have various clinical manifestations. Apart from pneumonia it can appear in the form of pharyngitis, laryngitis, bronchitis, otitis, rhinosinusitis [6]. Most frequently, even in 70–90% of cases, the infection is asymptomatic or with few symptoms [5–7]. The course of the infection may have the character of an acute infection, reinfection or chronic infection and is related to the immunological condition of the patient. In the situation when the immune system is not able to eliminate Chlamydia, the infection becomes a chronic process [8]. CP is capable of staying long and multiplying in infected cells. After entering human monocytes, CP becomes metaboli- cally active and it can participate in maintaining the local inflammatory and immune response [9]. In the course of an infection with CP a chronic antigen stimulation occurs which involves activation and proliferation of macrophages, lymphocytes, endothelial cells and the production of cytokines by these cells [1]. Moreover, lipopolysaccharides, which are a structural element of the cellular wall of bacteria, can enter the blood. They act in a non-specific way activating macrophages and stimulating them to synthesize pro-inflammatory cytokines, and

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control group (C) and the difference was statistical- ly significant (p = 0.03) (Fig. 1, Table I). The levels of IgG antibodies in both groups did not differ signi- ficantly (p = 0.96) (Fig. 2, Table I).

In the group with recent onset diabetes (R) IgM antibodies were significantly higher than IgG anti- bodies (p = 0.002) (Fig. 3, Table II).

The comparison of IgM antibodies between the group of children with long lasting diabetes (L) and the control group (C) did not reveal any significant difference (p = 0.13) (Fig. 1,Table I).

The difference of IgG antibodies between the groups was insignificant either (p = 0.07) (Fig. 2, Table I).

In the group with long lasting diabetes (L) the difference between IgM and IgG antibodies was not statistically significant (p = 0.17) (Fig. 3, Table II).

The comparison of IgG antibodies between the group with recent onset diabetes (R) and the group with long lasting diabetes (L) did not reveal any si- gnificant difference (p = 0.12) (Fig. 2, Table I).

variables. The significance of differences between the groups was assessed with Mann–Whitney test for non-parametric distribution. The value p < 0.05 was accepted as statistically significant.

Results

The level of serum IgM antibodies to CP was higher in the whole group of children with diabetes (D) than in the control group (C) and the diffe- rence was statistically significant (p = 0.03) (Fig. 1, Table I). The difference of serum IgG antibodies be- tween the groups was insignificant (p = 0.26) (Fig. 2, Table I).

In the whole group of children with diabetes (D) the difference between IgM and IgG antibodies was statistically significant (p = 0,001) (Fig. 3, Table II).

In the control group the difference between IgM and IgG antibodies was insignificant (p = 0.1) (Fig. 3, Table II).

The level of serum IgM antibodies in the group with recent onset diabetes (R) was higher than in the

Fig. 1. IgM levels in studied and control groups

Ryc. 1. Poziom IgM w grupach badanych i w grupie kontrolnej

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Table I. IgM and IgG levels in studied groups vs controls

Tabela I. Poziom IgM i IgG w grupach badanych vs grupa kontrolna Anti-

bodies Group p Group p Group p Group p

IgM

Diabetes (D)

Controls (C) 0.03

Recent onset diabetes (R)

Control (C) 0.03

Long lasting diabetes (L)

Control (C) 0.13

Recent onset diabetes (R) Long lasting diabetes (L)

0.20

IgG

Diabetes (D)

Controls (C) 0.26

Recent onset diabetes (R)

Control (C) 0.96

Long lasting diabetes (L)

Control (C)

0.07

Recent onset diabetes (R) Long lasting diabetes (L)

0.12

Fig. 2. IgG levels in studied and control groups

Ryc. 2. Poziom IgG w grupach badanych i w grupie kontrolnej

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Fig. 3. IgM and IgG levels in studied and control groups

Ryc. 3. Poziom IgM i IgG w grupach badanych i w grupie kontrolnej

Table II. Relation of IgM vs IgG levels in studied groups and controls Tabela II. Poziom IgM vs IgG w grupach badanych i w grupie kontrolnej

Group N Anti-bodies min

RU/ml max

RU/ml mediana

RU/ml p

Diabetes

(D) 47 IgM

IgG

0.10 1.10

22.9 12.9

5.40

3.90 0.001

Recent onset diabetes

(R) 23 IgM

IgG

0.80 1.10

22.9 10.4

6.30

3.10 0.002

lastingLong diabetes

(L)

24 IgM

IgG

0.10 1.80

13.2 12.9

4.90

4.35 0.17

Controls

(C) 37 IgM

IgG

0.42 0.20

16.6 21.2

4.40

2.90 0.1

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Discussion

Type 1 diabetes is a result of a chronic auto- immune process leading to damage to beta cells of the pancreatic islets. Despite extensive research, the cause and mechanism of autoaggression directed selectively against beta cells are still unclear. It is considered that the process of autodestruction is related to the action of environmental factors and the presence of genetic predisposition. Environmental factors (mainly viruses and also chemical and dietary factors) are thought to play a significant role in initiating the development of diabetes. The most recent research also concerns participation of bacteria and their toxins. Studies have appeared which indicate a relationship between bafilomycin A1 produced by Streptomyces spp. and an increase in the risk of developing type 1 diabetes [41, 42].

Research on the relationship between infection with Helicobacter pylori and diabetes did not bring positive results [43]. Yamaguchi et al. [44] examined a possible relationship between development of diabetes in non-obese diabetic (NOD) mice and dissemination of Chlamydia pneumoniae from the lung to peripheral blood. No influence of CP intranasal inoculation on development of diabetes in NOD mice was confirmed. However, there was significant difference in the lung inflammatory scores between diabetic and non-diabetic mice at the early stage after the infection. Also CP were more frequently detected in peripheral blood mononuclear cells in NOD mice than in mice without diabetes.

Muller et al. [45] measured the prevalence of Chlamydia pneumoniae DNA in peripheral blood mononuclear cells in patients with diabetes mellitus.

The prevalence of CP DNA was not significantly different in the patient group compared with the healthy subjects and no difference was found between type 1 and type 2 diabetes. There was, however, a positive correlation between the presence of CP DNA and high levels of triglycerides and CRP in diabetic patients.

Miettinen et al. [46] analysed a relationship between chlamydial infection and the risk of myocardial infarction or coronary death in diabetic and healthy subjects in Finland. They did not find any correlation between Chlamydia pneumonia antybodies and coronary heart disease events in diabetic patients.

Roubalova et al. [47] studied markers of Chla- mydia pneumoniae infection in patients with type 2

diabetes mellitus as possible predictors of cardiovas- cular complications. Anti- Chlamydia pneumoniae IgA, IgG or IgM were similar in both diabetic patients and controls, and CP DNA was not detected in the blood of any patient. In opposition, Altannavch [43] findings confirmed a relationship between CP and cardiovascular hart disease in diabetic patients with unstable angina pectoris.

Infections with CP affect all age groups although most authors consider them to be rare in the group of children below the age of 5 [32–35]. Recently Norman et al., using an immunohistochemical method, showed the presence of the CP antigen in the tonsils of all examined children aged 1 month to 5 years [36]. It seems that the results of examinations are related to sensitivity and specificity of the diagnostic method used [37]. In the population of children the first peak in high incidence of the disease is observed during the school years. However, in certain areas the infections are already common in children aged 1 to 4 [36, 38]. Infections with CP increase annually during the autumn–winter period.

Epidemics and endemics of the respiratory tract inflammations caused by this pathogen have been observed in Finland [39, 40].

In the studies that we conducted the level of serum IgM antibodies to CP was found to be significantly higher in the whole group of children with diabetes compared with the control group. In the group of children with recent onset diabetes the serum IgM antibodies to CP were either significantly higher than in the control group, being also significantly higher than IgG antibodies. In the group with long lasting diabetes IgG antibodies were higher than in the control group and the difference was considered close to significance (p = 0.07). An analysis conducted on a larger group of patients could possibly show the difference more precisely.

It is possible that a certain type of HLA system af- fects the modulation of the immunoinflammatory response induced by CP infection. Such observa- tions were made in Majorca where the relationship between CP infection and essential hypertension was studied [48].

Can infection with CP be an initial link in a chain of reactions leading to the development of a chronic immunoinflammatory response and possible further consequences in the form of beta cells destruction?

The answer to the question requires additional studies with a greater number of participants in a group and application of more specific diagnostic methods in order to assess infection with CP.

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[1] Everett K.D.: Chlamydia and Chlamydiales: more than meets the eye. Vet. Microbiol., 2000:75, 109-126.

[2] Campbell L.A., Cho-Chou K.: Chlamydia pneumonia pathogenezis. J. Med. Microbiol., 2000:51, 623-625.

[3] Bavoil P.M., Hsia R., Ojcius D.M.: Closing in on Chlamydia and its intracellular bag of tricks. Microbiology, 2000:146, 2723-2731.

[4] Hammerschlag M.R.: Chlamydia pneumoniae and the lung. Eur. Respir. J., 2000:16, 1001-1007.

[5] Kuo C.C.: Pathologic manifestation of chlamydial infection. Am. Heart J., 1999:138, 496-499.

[6] Tyl J.: Chlamydial infections of the respiratory tract in children. Przegl. Pediatr., 2003:33, 41-45.

[7] Miyashita N., Yoshihitob N., Nakajima M. et al.: Prevalence of asymptomatic infection with Chlamydia pneumoniae in subjectively healthy adults. Chest, 2001:119, 1416-1419.

[8] Kazar J., Kovacova E., Koncova K. et al.: Chlamydia pneumoniae antibodies and markers of inflammation in patients with cardiovascular diseases. Bratisl. Lek. Listy, 2005:106, 341-344.

[9] Airenne S., Surcel H.M., Alakarppa H. et al.: Chlamydia pneumoniae infection in human monocytes. Infect. Immun., 1999:67, 1445- 1449.

[10] Kosma P.: Chlamydial lipopolysaccharide. Biochim. Biophys. Acta, 1999:1455, 387-402.

[11] Kaukoranta-Tolvanen S.S., Teppo A.M., Leinonen M. et al.: Chlamydia pneumoniae induces the production of TNF-alfa, IL-1, and IL-6 by human monocytes. Proc. Eur. Soc. Chlamydia Res., 1992:2, 85-87.

[12] Huittinen T., Hahn D., Anttila T. et al.: Host immune response to Chlamydia pneumonia heat shock protein 60 is associated with asthma. Eur. Respir. J., 2001:17, 1078-1082.

[13] Black P.N., Scicchitano R., Jenkins C.R. et al.: Serological evidence of infection with Chlamydia pneumoniae is related to the severity of asthma. Eur. Respir. J., 2000:15, 254-259.

[14] Gern J.E.: Viral and bacterial infections in the development and progression of asthma. J. Allergy Clin. Immunol., 2000:105, 497- [15] Brouoard J., Freymuth F., Toutain F. et al.: Role of viral infections and Chlamydia pneumoniae and Mycoplasma pneumoniae 502.

infections in asthma in infants and young children. Epidemiologic study of 118 children. Arch. Pediatr., 2002:9, 365-371.

[16] Gencay M., Roth M.: Chlamydia pneumoniae infections in asthma: clinical implication. Am. J. Respir. Med., 2003:2, 31-38.

[17] Kuo C.C., Campbell L.A.: Detection of Chlamydia pneumoniae in arteria tissues. J. Infect. Dis., 2000:181, S432-S436.

[18] Blanc P., Corsi A.M., Gabbuti A.: Chlamydia pneumoniae seropositivity and cardiovascular risk factors: The InCHIANTI Study. JAGS, 2004:52, 1626-1631.

[19] Grayston J.T.: Background and current knowledge of Chlamydia pneumoniae and atherosclerosis. J. Infec. Dis., 2000:181, S402- S410.

[20] Dart A.M., Martin J.L., Kay S.: Association between past infection with Chlamydia pneumoniae and body mass index, low density lipoprotein particle size and fasting insulin. Int. J. Obes. Relat. Metab. Disord., 2002:26, 464-468.

[21] Laurila A., Anttila T., Laara E. et al.: Serological evidence of an association between Chlamydia pneumoniae infection and lung cancer. Int. J. Cancer, 1997:74, 31-34.

[22] Yucesan C., Sriram S.: Chlamydia pneumoniae infection of the central nervous system. Curr. Opin. Neurol., 2001:14, 355-359.

[23] Yao S.Y., Stratton C.W., Mitchell W.M. et al.: CSF oligoclonal bands in MS include antibodies against Chlamydophila antigens.

Neurology, 2001:56, 1168-1176.

[24] Balin B.J., Gerard H.C., Arking E.J. et al.: Identification and localization of Chlamydia pneumoniae in the Alzheimer’s brain. Med.

Microbiol. Immunol., 1998:187, 23-42.

[25] Airas L., Kotilainen P., Vainionpää R., Marttila R.J.: Encephalitis associated with Chlamydia pneumoniae. Neurology, 2001:56, 1778- 1779.

[26] Guglielminotti J., Lellouche N., Maury E. et al.: Severe meningoencephalitis: an unusual manifestation of Chlamydia pneumoniae infection. Clin. Infect. Dis., 2000:30, 209-210.

[27] Coste S., De Greslan T., Renard J.L.: Acute polyradiculoneuropathy after Chlamydia pneumoniae infection. Rev.

Neurol., 2002:158, 361-363.

[28] Madre J.G., Garcia J.L., Gonzales R.C. et al.: Association between seropositivity to Chlamydia pneumoniae and acute ischaemic stroke. Eur. J. Neurol., 2002:9, 303-306.

[29] Kanauchi M., Kawano T., Dohi K.: Association of Chlamydia pneumoniae infection with diabetic nephropathy. Diabetes.

Res. Clin. Pract., 2000:47, 45-48.

PIŚMIENNICTWO/REFERENCES

Conclusions

The significantly higher serum level of IgM antibodies to CP in the group with the recent onset type 1

diabetes compared to the control group as well as the significantly higher level of IgM antibodies than IgG found in this group may indicate a correlation between the CP infection and type 1 diabetes.

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[30] Furuta T., Saito T., Ootaka T. et al.: The role of macrophages in diabetic glomerulosclerosis. Am. J. Kidney Dis., 1993:

21, 480-485.

[31] Blans M.C., Visseren F.L., Banga J.D. et al.: Infection induced inflammation is associated with erectile dysfunction in men with diabetes. Eur. J. Clin. Invest., 2006:36, 497-502.

[32] Lammi N., Karvonen M., Tuomilehto J.: Do microbes have a causal role in type 1 diabetes. Med. Sci. Monitor, 2005:

11, 63-69.

[33] Myers M.A., Hettiarachchi K.D., Ludeman J.P. et al.: Dietary microbial toxins and type 1 diabetes. Ann. NY Acad. Sci., 2003:1005, 418-422.

[34] Altannavch T., Roubalová K., Broz J. et al.: Serological markers of Chlamydia pneumoniae, cytomegalovirus and Heli- cobacter pylori infection in diabetic and non-diabetic patients with unstable angina pectoris. Cent. Eur. J. Public Health, 2003:11, 102-106.

[35] Yamaguchi H., Oschio I., Osaki T. et al.: Development of diabetes in non-obese diabetic mice promotes Chlamydia pneumonia dissemination from lung to peripheral blood. Int. J. Exp. Path., 2006:87, 121-129.

[36] Müller J., Møller D.S., Kjær M. et al.: Chlamydia pneumoniae DNA in Peripheral Blood Mononuclear Cells in Healthy Control Subjects and Patients with Diabetes mellitus, Acute Coronary Syndrome, Stroke, and Arterial Hypertension.

Scand. J. Infect. Dis., 2003:35, 704-712.

[37] Miettinen H., Lehto S., Saikku P. et al.: Association of Chlamydia pneumoniae and acute heart disease events in non-in- sulin dependent diabetic and non-diabetic subjects in Finland. Eur. Heart J., 1996:17, 682-688.

[38] Roubalová K., Broz J., Hrubá D.: Prevalence of active infection with Chlamydia pneumoniae and human cytomegalovi- rus in patients with type II diabetes mellitus. Folia Microbiol. (Praha), 2007:52, 287-290.

[39] Wubbel L., Muniz L., Ahmed A. et al.: Etiology and treatment of community-acquired pneumonia in ambulatory children. Pediatr. Infect. Dis. J., 1999:18, 98-104.

[40] Heiskanen-Kosma T., Korppi M., Laurila A. et al.: Chlamydia pneumoniae is an important cause of community-acqu- ired pneumonia in school-aged children: serological results of a prospective, population-based study. Scan. J. Infect.

Dis., 1999:31, 255-259.

[41] Stawarski A., Choroszy-Król I., Iwańczak B. et al.: Epidemiology of atypical pneumonia caused by Mycoplasmapneu- moniae and Chlamydia sp. in children. Adv. Clin. Exp. Med., 2001:10, 37-44.

[42] Principi N., Esposito S., Blasi F. et al.: Role of Mycoplasma pneumoniae and Chlamydia pneumoniae in children with community-acquired lower respiratory tract infections. Clin. Infect. Dis., 2001:32, 1281-1289.

[43] Norman E., Gnarpe J., Nääs J. et al.: Chlamydia pneumoniae in children undergoing adenoidectomy. Acta Paediatr., 2001:90, 126-129.

[44] Dowell S., Peeling R., Boman J. et al.: Standarizing Chlamydia pneumonia Assays: Recommendations from the Cen- ters for Disease Control and Prevention (USA) and the Laboratory Centre for Disease Control (Canada). Clin. Infec. Dis., 2001:33, 492-503.

[45] Gendrel D.: Intracellular pathogens and asthma: Mycoplasma pneumoniae and Chlamydia pneumoniae in paediatric patients. Eur. Respir. Rev., 1996:38, 231-234.

[46] Ekman M.R., Leinonen M., Syrjala H. et al.: Evaluation of serological methods in the diagnosis of Chlamydia pneumo- nia during an epidemic in Finland. Eur. J. Clin. Microbiol. Infect. Dis., 1993:12, 756-760.

[47] Kauppinen M.T., Herva E., Kujula P.: The etiology of community-acquired pneumonia among hospitalised patients du- ring a Chlamydia pneumoniae epidemic in Finland. J. Infect. Dis., 1995:172, 1330-1335.

[48] Zabay J.M., Marco J., Soler J. et al.: Association of HLA-DRB3*0202 and serum IgG antibodies to Chlamydia pneumo- niae with essential hypertension in a highly homogenous population from Majorca (Balearic Islands, Spain). J. Hum.

Hyper., 2005:19, 615-622.