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Mannan-binding lectin and C1q bind to distinct structures and exert differential effects on macrophages

Z Bajtay1, M Józsi, Z Bánki

  • 1Department of Immunology and Hungarian Academy of Sciences, Eötvös Loránd University, Göd.

European Journal of Immunology
|July 18, 2000
PubMed

Insights

Mannan-binding lectin (MBL) binds selectively to macrophages, unlike complement component C1q. This differential binding affects immune responses, with C1q, but not MBL, inducing TNF-alpha release and robust complement C3 production.

Area of Science:

  • Immunology
  • Molecular Biology

Background:

  • Complement component C1q interactions with cellular proteins are well-documented.
  • The binding of structurally similar mannan-binding lectin (MBL) to cells is less understood.

Purpose of the Study:

  • To investigate and compare the cellular binding patterns of MBL and C1q.
  • To explore the functional consequences of MBL and C1q interactions with immunocompetent cells.

Main Methods:

  • Cytofluorimetry was used to assess MBL and C1q binding to human monocyte-derived macrophages (Mphi), monocytoid cell lines, T lymphocytes, and B lymphocytes.
  • Functional assays measured TNF-alpha release and complement C3 production by Mphi.
  • Red blood cell (RBC) opsonization and phagocytosis were evaluated.

Main Results:

  • MBL selectively binds to Mphi and monocytoid cell lines at physiological ionic strength, while C1q interacts with Mphi, monocytoid cell lines, T, and B lymphocytes.
  • Low ionic strength did not enhance MBL binding to Mphi.
  • MBL and C1q do not compete for the same cellular binding sites.
  • C1q induced TNF-alpha release and strong C3 production in Mphi, whereas MBL had a weaker effect on C3 production and did not induce TNF-alpha release.
  • C1q-mediated C3 production enhanced RBC opsonization and phagocytosis.

Conclusions:

  • Cellular binding molecules for MBL and C1q are distinct.
  • MBL and C1q exert significantly different biological functions on immunocompetent cells.

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