Lymphocyte Response in Subjects with Chronic Pulmonary Disease Colonized by Pneumocystis jirovecii

Pneumocystis jirovecii, known also by its interim trinomial name as Pneumocystis carinii f. sp. hominis [1], continues to be one of the most important causes of opportunistic infections in AIDS patients and in HIV-negative immunocompromised patients [2]. The incidence of P. jirovecii pneumonia (PcP) has decreased in AIDS patients in developed countries with the use of specific chemoprophylaxis and, above all, with highly active antiretroviral therapy. In spite of this, PcP is still an important cause of morbidity and mortality in the western world and is a problem that is being identified more and more in developing countries [3]. Nowadays, interest in P. jirovecii infection is not confined to AIDS patients alone; it also represents a common and serious opportunistic infection in HIV-negative immunocompromised patients due to different causes, such as organ transplant recipients [4], patients with autoimmune diseases who receive immunosuppressive therapy [5], or patients with neoplasias, especially in those with lymphoproliferative diseases [6]. On the other hand, pneumonia caused by this microorganism is not limited to immunosuppressed patients; but, it can affect subjects with no apparent immunosuppression, as it has been well documented in recent publications, describing a series of PcP patients without evidence of immunodeficiency [7,8,9]. Moreover immunocompetent subjects without PcP can be colonized by the pathogen. In this sense, Pneumocystis carriage was found in 10–40% of patients with chronic obstructive disease [10–11]. The major predisposing factor for the development of PcP is impaired cell mediatedor humoral immune response [12]. In patients with HIV infection or T cell defects, the CD4þ T lymphocytes have been shown to play a major role in the defense against this infection. In fact PcP often occurs in AIDS patients with a severe lymphopenia and less that 200 CD4þ T lymphocytes/ml [13]. However, it is not known what changes occur in the lymphocyte response in immunocompetent subjects colonized by this pathogen. The aim of this initial study was to provide information on the lymphocyte response in immunocompetent patients who are colonized by P. jirovecii.