Related Experiment Videos
Interactions of Neisseria meningitidis with human monocytes
1Department of Paediatrics, University of Oxford, John Radcliffe Hospital, U.K.
Abstract:
The roles of capsule, pili and Class 5 outer-membrane proteins (Opa and Opc) of Neisseria meningitidis (Nm) in bacterial interactions with human monocytes were investigated using several meningococcal isolates of different serogroups. The presence of either Class I or Class II pili in capsulate strains of several serogroups had no significant effect on adherence to and internalisation by monocytes. Using clonal variants derived from a non-piliated serogroup A strain, C751, it was observed that capsulate bacteria (cap+) failed to interact with human monocytes in significant numbers whether or not they expressed outer-membrane proteins. These bacteria were also resistant to phagocytic killing. For capsule-deficient bacteria, expression of the Opc protein or OpaBC751 correlated with high levels of association, while the expression of OpaDC751 or OpaAC751 resulted in comparatively lower levels. Bacteria expressing undetectable levels of Opc or Opa proteins (Opc-, Opa-) failed to interact with monocytes. In phagocytic killing assays, Opc-expressing bacteria (Opc+) as well as Opa-expressing bacteria (Opa+) were killed more readily than Opc-, Opa- bacteria (30% decrease in viability of Opc+ bacteria; 18%, 10% and 8% decrease in viability of OpaB+, OpaD+ and OpaA+ bacteria). A study of intracellular survival showed a gradual decrease in viability of both capsulate and capsule-deficient bacteria. However, proportionately greater numbers of capsule-deficient bacteria were internalized and consequently larger numbers survived over a 4-h period. Prolonged bacterial survival within phagocytic cells may have implications in dissemination of bacteria by carriage within these cells.
Insights
Neisseria meningitidis capsule protects against monocyte interaction and killing. Capsule-deficient bacteria expressing Opc or Opa proteins show varied interactions and increased killing, but enhanced intracellular survival.
Area of Science:
- Microbiology
- Immunology
- Bacterial Pathogenesis
Background:
- Neisseria meningitidis (Nm) is a significant human pathogen.
- Bacterial surface structures play crucial roles in host-pathogen interactions.
- Understanding interactions with immune cells like monocytes is key to pathogenesis.
Purpose of the Study:
- To investigate the roles of capsule, pili, and outer-membrane proteins (Opa, Opc) of N. meningitidis in interactions with human monocytes.
- To determine how these factors influence bacterial adherence, internalization, and survival within monocytes.
Main Methods:
- Utilized various meningococcal isolates from different serogroups.
- Employed clonal variants of a serogroup A strain (C751) with defined surface protein expression.
- Conducted adherence, internalization, and phagocytic killing assays with human monocytes.
Main Results:
- Capsule presence significantly hindered monocyte interaction and conferred resistance to phagocytic killing.
- Pili (Class I or II) had no significant effect on monocyte interactions in capsulate strains.
- In capsule-deficient strains, Opc and OpaBC751 expression correlated with high monocyte association, while OpaD and OpaA showed lower association; Opc+, Opa+ bacteria were killed more readily, but capsule-deficient bacteria showed greater intracellular survival.
Conclusions:
- The bacterial capsule is a major factor preventing early interaction with monocytes and promoting resistance to killing.
- Outer-membrane proteins Opc and Opa modulate interactions of capsule-deficient N. meningitidis with monocytes.
- Intracellular survival of capsule-deficient meningococci within monocytes may contribute to bacterial dissemination.