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Involvement of C3a and C5a in interleukin-8 secretion by human polymorphonuclear cells in response to capsular
A Vecchiarelli1, C Retini, A Casadevall
1Microbiology Section, Department of Experimental Medicine and Biochemical Sciences, University of Perugia, 06122 Perugia, Italy. vecchiar@unipg.it
Abstract:
In a previous paper we demonstrated that human polymorphonuclear cells (PMN) in the presence of normal human serum (NHS) secrete proinflammatory cytokines in response to Cryptococcus neoformans or its major capsular component, glucuronoxylomannan (GXM). The hypothesis that activation of the complement system could be responsible for the observed phenomenon is supported by the fact that encapsulated and acapsular C. neoformans isolates are activators of the complement system and, in particular, large encapsulated isolates are powerful activators. In the present study we demonstrate that (i) interleukin-8 (IL-8) release in response to acapsular or encapsulated strains of C. neoformans is significantly reduced in the presence of heat-inactivated serum rather than NHS and is completely abrogated in the absence of human serum; (ii) GXM-induced IL-8 release is strictly dependent on the presence of NHS, is inhibited by specific antibodies to either C3a and C5 complement components, and is completely abrogated by the combined use of these antibodies; (iii) the addition of purified C3a and C5a directly stimulates IL-8 release by PMN; and (iv) monoclonal antibody to GXM in combination with GXM or encapsulated C. neoformans potentiates IL-8 release by PMN. These data shed light on the mechanism involved in GXM-induced IL-8 secretion by PMN, provide an additional potential role for complement in the control of C. neoformans infections, and suggest a complex interplay between the complement system, humoral immunity, and cytokine regulation.
Insights
Human immune cells release inflammatory cytokines when encountering Cryptococcus neoformans. Complement system activation, specifically C3a and C5a, is crucial for this response, highlighting its role in fungal infections.
Area of Science:
- Immunology
- Microbiology
- Infectious Diseases
Background:
- Human polymorphonuclear cells (PMN) secrete proinflammatory cytokines in response to Cryptococcus neoformans and its capsular component, glucuronoxylomannan (GXM).
- Encapsulated and acapsular C. neoformans strains activate the complement system, suggesting its involvement in PMN activation.
Purpose of the Study:
- To investigate the role of the complement system in mediating interleukin-8 (IL-8) release by PMN in response to C. neoformans and GXM.
- To elucidate the specific complement components involved in GXM-induced IL-8 secretion.
Main Methods:
- Assessing IL-8 release from PMN incubated with C. neoformans strains or GXM in the presence of normal human serum (NHS), heat-inactivated serum, or serum-deficient media.
- Utilizing antibodies against complement components C3a and C5a to inhibit GXM-induced IL-8 release.
- Testing the direct effect of purified C3a and C5a on PMN IL-8 secretion.
- Evaluating the potentiation of IL-8 release by monoclonal antibodies against GXM.
Main Results:
- IL-8 release was significantly reduced with heat-inactivated serum and abrogated without serum, indicating serum dependence.
- GXM-induced IL-8 release was dependent on NHS and inhibited by antibodies to C3a and C5a, with complete abrogation by combined antibodies.
- Purified C3a and C5a directly stimulated IL-8 release from PMN.
- Monoclonal antibodies to GXM potentiated GXM or encapsulated C. neoformans-induced IL-8 release.
Conclusions:
- Complement activation, particularly via C3a and C5a, is a key mechanism driving IL-8 secretion by PMN in response to C. neoformans and GXM.
- The complement system plays a significant role in the host's immune response to C. neoformans infections.
- A complex interplay exists between the complement system, humoral immunity, and cytokine regulation in C. neoformans pathogenesis.