Chapter 7. Conclusions

The findings of this study show an association of IgA antibodies to the Hsp60 protein of C. pneumoniae with asthma and thereby provide further support for the association between C. pneumoniae infection and asthma. Moreover, the results show, for the first time, that low-grade systemic inflammation, demonstrated as a slightly elevated CRP level, was present in stable asthma, despite therapy with inhaled corticosteroids. The CRP levels were higher among the patients with moderate asthma than among the patients with mild asthma. Serum IgA antibodies to the Hsp60 protein of C. pneumoniae and the whole C. pneumoniae were both associated with an elevated CRP level. These findings support the theory that, in some asthma patients, inflammation might be a consequence of chronic C. pneumoniae infection and immune reactions to this infectious agent.

The findings of this study show that IgA antibodies against human Hsp60 and C. pneumoniae as well as slightly elevated CRP concentration were all risk factors for coronary events, especially when elevated persistently, not transiently. The coronary risk associated with elevated antibody levels increased considerably in the presence of an elevated CRP level and vice versa. The risk was increased by an increasing number of persistently elevated risk factors, being highest when all the three factors were elevated. Thus, it seems that chronic infection, autoimmunity and inflammation together caused coronary events in this study population. The speculative pathway in the case of C. pneumoniae infection is initiated by a chain reaction in which CRP and Hsp60 play a role: a chronic C. pneumoniae infection increases the expression of its own Hsp60, which leads to an increased expression of host Hsp60 and thus gradually results in autoimmunity with systemic inflammation and elevated CRP and, finally, clinical manifestations of CHD.

In conclusion, these results suggest that Hsp60 of C. pneumoniae is involved in the association between C. pneumoniae infection and asthma, while autoimmunity to human Hsp60 is implicated in the association between C. pneumoniae infection and CHD. Inflammation evidently has an important role within these associations. It can also be concluded that IgA antibodies, compared to IgG antibodies, against C. pneumoniae and Hsp60 are better markers of chronicity, especially when they are persistently elevated. Further research is warranted to clarify the role of Hsp60 proteins, C. pneumoniae infection and CRP in the pathogenesis of these diseases.