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Human colostral cells. I. Separation and characterization
Insights
Human colostrum contains approximately 3.3 million cells per ml, primarily macrophages and polymorphonuclear leukocytes. These phagocytic cells ingest lipids and milk proteins, but lymphoid cells do not.
Area of Science:
- Immunology
- Cell Biology
- Lactation Biology
Background:
- Human colostrum is a crucial source of immune factors for newborns.
- Understanding the cellular composition and function of colostrum is vital for infant health.
- Previous characterization of colostral cells has been limited.
Purpose of the Study:
- To comprehensively analyze the cell types and their protein content in early human colostrum.
- To investigate the origin and function of proteins within colostral cells.
- To evaluate the reliability of standard lymphocyte identification markers in colostrum.
Main Methods:
- Analysis of colostrum from 54 healthy donors using histochemical and immunohistochemical staining.
- Cell separation techniques including density centrifugation and adherence.
- Detection of specific proteins (immunoglobulins, secretory component, lactoferrin, alpha-lactalbumin) and lipids within cells.
Main Results:
- Colostrum contains 3.3 x 10^6 cells/ml, predominantly macrophages (30-47%) and polymorphonuclear leukocytes (40-60%).
- Phagocytic cells (macrophages, polymorphonuclear leukocytes, colostral corpuscles) contain lipids and various milk proteins, acquired through ingestion.
- Standard lymphocyte markers were unreliable; lymphocytes were classified as T cells based on association with other cells.
Conclusions:
- Human colostrum harbors a significant population of phagocytic cells actively involved in protein and lipid uptake.
- The presence of ingested proteins within phagocytic cells highlights their role in nutrient and immune transfer.
- Morphological characterization is essential for accurate cell identification in colostrum due to limitations of standard markers.
Abstract:
Analyses of the cells present in human colostrum obtained from fifty-four healthy donors during the first four days of lactation revealed that there were 3.3 x 10(6) (range 1.1 x 10(5)--1.2 x 10(7)) cells per ml of colostrum. Based on histochemical examinations, it was found that this population consisted of 30--47% macrophages, 40--60% polymorphonuclear leucocytes, 5.2--8.9% lymphocytes, and 1.3--2.8% colostral corpuscles; epithelial cells were rarely encountered. The identity of various cell types was confirmed by Wright's stain and by a series of histochemical techniques which disclosed the presence of non-specific esterase, peroxidase, and lipids. For further characterization, the different types of cells were separated by various methods, such as Ficoll-Hypaque density centrifugation, isokinetic centrifugation on a linear Ficoll gradient, adherence to glass or plastic, and phagocytosis of carbonyl iron. Immunohistochemical staining with FITC- and/or TRITC-labelled reagents to IgA, IgM, IgG, K- and lambda-chains, secretory component, lactoferrin, and alpha-lactalbumin were applied to unseparated as well as separated colostral cells. Polymorphonuclear leucocytes (staining for peroxidase) as well as macrophages and colostral corpuscles (staining for non-specific esterase) exhibited numerous intracellular vesicles that contained lipids as well as various combinations of milk proteins. Lymphoid cells did not stain with any of these reagents and plasma cells were not detected among the colostral cells. Individual phagocytic cells contained immunoglobulins of the IgA and IgM classes, both K and lambda light chains, secretory component, lactoferrin, and alpha-lactalbumin. The coincidental appearance of these proteins in single, phagocytic cells but not in lymphoid cells indicate that the cells acquired these proteins by ingestion from the environment. Markers commonly used for the identification of B lymphocytes (surface immunoglobulins) and T lymphocytes (receptors for sheep red blood cells) were unreliable for the analysis of colostral cells (unless accompanied by subsequent morphological characterization) because strong fluorescence was observed on the surface of many non-lymphoid cells and because numerous macrophages and colostral corpuscles formed rosettes with sheep red blood cells (SRBC). Lymphocytes, often found in association with colostral macrophages or corpuscles, were classified as T cells.