Related Experiment Videos
Binding ability of complement receptor CR1 to C3 bound on the surface of M+ group A streptococci
K Hong1, T Harada, T Nishimura
1Department of Bacteriology, Osaka University Medical School, Japan.
Abstract:
A previous study demonstrated that although M+ bacteria bound C3, mainly C3b and iC3b, via the classical pathway of complement activation, they were not phagocytosed by polymorphonuclear leucocytes (PMN). To elucidate this mechanism, we attempted to distinguish between the possibilities that M+ bacteria are effectively adhering to PMN but are not being endocytosed, or that the C3 deposited on M+ bacteria is not able to interact with the complement receptors on PMN. In the present study, we studied the interaction of C3-coated M+ bacteria with complement receptor CR1, which was isolated from the stroma of human erythrocytes. We show that the isolated complement receptor CR1 can associate with C3-coated M+ bacteria as well as with C3-coated M- bacteria, and the C3 deposited on M+ bacteria is cleaved and releases a C3 fragment in the presence of factor I and liquid-phase CR1. These results suggest that the C3 bound on the surface of M+ bacteria is able to promote adherence to the complement receptor CR1 on PMN. We also studied the distribution of C3 deposited on M+ bacteria in normal human serum (NHS) or normal human plasma (NHP). By immunofluorescence, we show that the C3 bound to M+ bacteria in NHS was deposited uniformly over the surface of the bacteria. On the other hand, the C3 bound to M+ bacteria in NHP was deposited at both ends between adjacent daughter cocci. The results suggest that an additional factor contained in NHP is related to the enhancement of anti-phagocytic activity of M+ bacteria.
Insights
Complement-coated bacteria (M+ bacteria) can adhere to polymorphonuclear leucocytes (PMN) via complement receptor CR1. However, specific C3 deposition patterns in normal human plasma may enhance M+ bacteria's anti-phagocytic activity.
Area of Science:
- Immunology
- Microbiology
Background:
- Previous studies showed M+ bacteria bind complement component 3 (C3) but resist phagocytosis by polymorphonuclear leucocytes (PMN).
- The mechanism behind this resistance, whether it's poor adherence or impaired C3-receptor interaction, was unclear.
Purpose of the Study:
- To investigate the interaction between C3-coated M+ bacteria and complement receptor CR1 (CR1) on PMN.
- To determine if C3 deposited on M+ bacteria can interact with PMN complement receptors.
- To analyze the distribution of C3 on M+ bacteria in different human serum/plasma conditions and its effect on anti-phagocytic activity.
Main Methods:
- Studied the interaction of C3-coated M+ bacteria with isolated human erythrocyte CR1.
- Investigated C3 fragment release from M+ bacteria-bound C3 using factor I and liquid-phase CR1.
- Analyzed C3 deposition patterns on M+ bacteria in normal human serum (NHS) and normal human plasma (NHP) using immunofluorescence.
Main Results:
- Isolated CR1 associated with both C3-coated M+ and M- bacteria.
- C3 on M+ bacteria was cleaved, releasing C3 fragments in the presence of factor I and CR1, suggesting adherence promotion.
- Immunofluorescence revealed uniform C3 deposition in NHS, but end-specific deposition in NHP, correlating with enhanced anti-phagocytic activity.
Conclusions:
- Bound C3 on M+ bacteria can facilitate adherence to PMN via CR1.
- NHP contains a factor that alters C3 deposition, potentially enhancing the anti-phagocytic properties of M+ bacteria.