Localization of IgA and IgM in human colostral elements using immunoelectron microscopy

Area of Science:

• Immunology
• Cell Biology
• Human Colostrum Research

Background:

• Immunoglobulin A (IgA) is a key component of human colostrum, but its cellular localization has been debated.
• Understanding IgA distribution is crucial for comprehending its role in neonatal immunity.

Purpose of the Study:

• To resolve controversy regarding the specific cell types containing IgA in human colostrum.
• To investigate the distribution of IgA and Immunoglobulin M (IgM) within colostral elements using advanced microscopy.

Main Methods:

• Immunoelectron microscopy utilized horseradish peroxidase-labeled antibody fragments (F(ab')2 or Fab') against IgA and IgM.
• Localization of immunoglobulins within phagocytic vacuoles of polymorphonuclear leukocytes and macrophages.
• In vitro phagocytosis assays with colloidal gold particles to assess cellular uptake.

Main Results:

• IgA and IgM were localized within phagocytic vacuoles of polymorphonuclear leukocytes and macrophages.
• These immunoglobulins were also found in noncellular colostral globules.
• Lymphocytes and plasma cells in colostrum did not contain detectable levels of IgA or IgM.

Conclusions:

• Colostral IgA and IgM are acquired by phagocytic cells and noncellular globules, not synthesized by lymphoid cells present.
• Phagocytic cells in colostrum demonstrate uptake capabilities, internalizing IgA and IgM.
• Findings clarify the origin and distribution of key immunoglobulins in early human milk.