Host-pathogen relationships in respiratory tract infections
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1Department of Clinical Microbiology and Infectious Diseases, University Hospital Utrecht, The Netherlands.
Abstract:
The respiratory tract is continuously exposed to inhaled particles. The mucous membrane and the mechanisms of sneezing, coughing, and mucociliary clearance are the first line of defense. For the bronchioli and alveoli, the phagocytic cells are the cornerstone of defense against invading microorganisms. Alveolar macrophages and polymorphonuclear leukocytes are responsible for phagocytosis. For optimal phagocytosis, antibodies and complement are needed; phagocytic cells possess receptors for the Fc fragment of the immunoglobulin (IgG) molecule and complement. Receptors for cytokines are also present. These cytokines are important for activating the alveolar macrophage and recruiting other phagocytic cells and lymphocytes to the site of infection. Alveolar macrophages also contain cytophilic antibodies, IgG molecules that are bound to the cell via the F(ab)2 fragments. These cytophilic antibodies can interfere with the process of phagocytosis. They can bind to bacteria containing an Fc receptor (eg, Staphylococcus aureus protein A) and therefore provide the alveolar macrophage with a means to bind and digest staphylococci. Pulmonary surfactant proteins enhance the uptake of bacteria and viruses by alveolar macrophages and viruses. Thus surfactant contributes to the defense mechanisms of the lung. Phagocytic cells can injure alveoli. During the process of phagocytosis, toxic oxygen species and enzymes, needed for killing bacteria, are produced. These toxic substances may leak out of the cell and damage the surrounding tissues. All these phenomena contribute to the processes of inflammation. The function of phagocytic cells is decreased in smokers and by certain air pollutants. Phagocytic cells are crucial for the elimination of microorganisms.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Phagocytic cells, like alveolar macrophages, are vital for lung defense against inhaled particles and microbes. Their function is impaired by smoking and air pollution, impacting overall respiratory health.
Area of Science:
- Immunology
- Pulmonology
- Cell Biology
Background:
- The respiratory tract's initial defense involves physical barriers and clearance mechanisms.
- Deeper lung structures rely on phagocytic cells, primarily alveolar macrophages and polymorphonuclear leukocytes, for microbial defense.
Purpose of the Study:
- To elucidate the multifaceted role of phagocytic cells in lung immunity.
- To explore the mechanisms of phagocytosis, including the involvement of antibodies, complement, and cytokines.
- To investigate factors affecting phagocytic cell function and potential self-damaging effects.
Main Methods:
- Review of the literature on lung defense mechanisms.
- Analysis of the molecular interactions involved in phagocytosis (e.g., Fc receptors, cytokine receptors).
- Examination of the role of pulmonary surfactant proteins and cytophilic antibodies.
Main Results:
- Phagocytic cells utilize antibodies (immunoglobulin G) and complement for efficient microbial clearance.
- Cytokines are crucial for activating and recruiting phagocytic cells to infection sites.
- Pulmonary surfactant proteins enhance microbial uptake by alveolar macrophages.
- Cytophilic antibodies can facilitate bacterial binding and digestion, while also potentially interfering with phagocytosis.
- Phagocytic cells can cause tissue damage through the release of toxic substances during microbial killing, contributing to inflammation.
- Phagocytic cell function is compromised in smokers and by exposure to air pollutants.
Conclusions:
- Phagocytic cells are essential for eliminating microorganisms in the lungs.
- Factors such as smoking, air pollution, and specific antibody interactions can modulate phagocytic cell efficacy and contribute to lung pathology.