Purification and properties of human lymphocyte activating factor (LAF)

Area of Science:

• Immunology
• Cell Biology

Background:

• Lymphocyte-activating factor (LAF) production is primarily associated with LPS-stimulated human monocytes and leukocytes.
• Non-macrophage cell lines generally do not produce LAF, suggesting cell-type specificity.
• Macrophage activators like latex microspheres and antigen-antibody complexes also induce LAF production.

Purpose of the Study:

• To characterize the production and purification of Lymphocyte-activating factor (LAF).
• To investigate the biological activity of purified LAF on thymocytes.
• To explore factors influencing thymocyte responsiveness to LAF.

Main Methods:

• LAF production induced by various stimuli in human adherent cells and leukocytes.
• Chromatographic techniques (Sephadex G-100, anion exchange, adsorption) for LAF purification.
• Assay of LAF-induced thymocyte mitosis and sensitivity to enzymatic and chemical treatments.

Main Results:

• LAF activity appears after a 6-hour delay, peaking at 12-24 hours.
• Purification revealed two active peaks (85,000 and 13,000 daltons), with the smaller one being major and purified >500-fold.
• Purified LAF induced mitosis in 10% of murine thymocytes and was chymotrypsin-sensitive but unaffected by other tested reagents.
• Thymocyte responsiveness to LAF decreased with age and increased in cortisone-treated or tumor-bearing animals.

Conclusions:

• LAF is a distinct factor produced by activated monocytes/leukocytes with specific molecular properties.
• Purified LAF possesses mitogenic activity for thymocytes.
• Thymocyte response to LAF is modulated by age and specific immune conditions, indicating complex regulatory mechanisms.