The Existence Of T Helper (Tμ) And T Suppressor (Tγ) Cells For The Generation Of Monocyte Thromboplastin Activity By Lipopolysaccharides

Human peripheral blood mononuclear cells (PBM) in response to LPS stimulation generate increased quantities of thromboplastin activity. Monocytes are the cellular source of this activity and direct lymphocyte collaboration is required for its expression. PBM were separated by adherence into monocyte and lymphocyte fractions. Lymphocytes were further fractionated into T and non-T cells by rosetting with neuraminidase treated SRBC. 1 × 10⁵ monocytes had a basal activity of 250 mU which increased to a maximum 2850 mU when monocytes were stimulated by 10 ug LPS for 6 hrs at a T cell: monocyte ratio of 4:1. No increase in thromboplastin activity was observed when monocytes were stimulated by LPS either alone or in the presence of non-T cells. Moretta et al. have described a system in which T cells are segregated into helper and suppressor subsets according to their ability to mediate immunoglobulin synthesis in response to pokeweed mitogen (PWM) stimulation. Using this system, T cells were further subfractionated into helper (T_μ), suppressor (T_γ ) and T null cells by cytoadherence to IgM or IgG coated ox RBC. 1 × 10⁵ monocytes when incubated with increasing numbers of T_μ cells generated a maximal 4150 mU thromboplastin activity as the ratio of T_μ: monocytes approached 4:1. No increase in monocyte thromboplastin activity was observed above basal levels of 160 mU when monocytes were stimulated by LPS in the presence of either T_γ or T null cells. T_γ cells were observed to suppress T_μ helper cell function with a decrease in monocyte thromboplastin activity from 4150 mU to 1100 mU as the T_γ: T_μ ratio increased from 0:1 to 4:1. Thus, at least two populations within the T lymphocyte series the T _μ (helper) and T_γ (suppressor) fractions modulate the expression of thromboplastin activity by monocytes.