The initial characterization of a thymus factor chemotactic to bone marrow cells

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• The thymus is crucial for T-cell maturation, requiring the homing of progenitor cells from bone marrow.
• The molecular mechanisms guiding immature lymphoid cell migration to the thymus are not fully elucidated.
• Thymus-derived factors are implicated in regulating this homing process.

Purpose of the Study:

• To characterize the chemotactic factor(s) present in thymus supernatants responsible for bone marrow cell migration.
• To compare the activity of thymus supernatants with known thymic factors like thymulin and thymopoietin.
• To investigate the biochemical properties of the active chemotactic factor.

Main Methods:

• Preparation of thymus supernatants from minced newborn mouse thymuses.
• Chemotaxis assays using blind well chambers to assess bone marrow cell migration.
• In vitro characterization including heat stability, enzymatic digestion (trypsin, chymotrypsin), and molecular weight fractionation (Amicon microconcentrators).

Main Results:

• Thymus supernatants exhibited chemotactic activity for a subset of bone marrow cells, enriching for immature lymphoid cells.
• Known thymic factors (thymulin, FTS-Zn, FTS, TP-5) did not show chemotactic activity in the tested concentrations.
• The chemotactic activity was partially heat-stable (50% decrease at 100°C for 1h) and inhibited by chymotrypsin but not trypsin.
• Molecular weight fractionation indicated the active factor is likely less than 10,000 Da.

Conclusions:

• A novel chemotactic factor distinct from previously characterized thymic hormones exists in thymus supernatants.
• This factor plays a role in attracting immature lymphoid cells, potentially guiding their homing to the thymus.
• The factor's biochemical properties suggest it is a peptide or protein susceptible to chymotrypsin degradation.