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Capping of the surface OKT3 binding molecule prevents the T-cell proliferative response to antigens: evidence that
Abstract:
The human T-lymphocyte receptor for antigen appears to have been localized to a cluster of associated surface glycoprotein molecules, among which is the OKT3 binding molecule. We have tested the hypothesis that selective removal of the OKT3 binding molecule eliminates the cellular immune response to antigens by clearing the surface of the molecule that conveys the activation signal. Enriched T cells were obtained from donors immune to purified protein derivative (PPD), streptokinase-streptodornase (SK-SD), or keyhole limpet hemocyanin (KLH). T-3 molecules were cleared from the cell surface by capping with OKT3 and F(ab')2 goat anti-mouse IgG. Regeneration of surface molecules was prevented by culturing the T-3 capped cells with OKT3 625 ng/ml. The capacity of capped T cells to proliferate in culture with antibody in response to antigens, alloantigens, and the mitogens, PHA and ionophore A23187, was compared to uncapped cells pretreated with media and to capped cells permitted to regenerate the OKT3 binding molecule. T-3 capped cells cultured in the presence of antibody failed to proliferate to antigens or alloantigens. However, T-3 capped cells cocultured with antibody also did not significantly proliferate to PHA, but did respond to A23187. In contrast, both media-treated T cells and cells which had regenerated the OKT3 binding molecule proliferated to mitogens, antigens, or alloantigens. The requirement for the OKT3 binding molecule was determined by utilizing T-1, T-4, and T-8 capped cells. T-1, T-4, or T-8 capped cells cultured in the presence of OKT1, OKT4, or OKT8 proliferated in response to antigens, alloantigens, and mitogens. These results demonstrate that in the absence of the OKT3 binding molecule, antigens, alloantigens, and PHA failed to induce a significant cellular proliferative response. In the absence of this molecule, PHA cannot bind to its carbohydrate moiety, and therefore cannot activate T cells to proliferate. These data support the concept that the molecule binding OKT3 conveys the transmembrane signal resulting in cellular activation.
Insights
Removing the OKT3 binding molecule from T cells blocks immune responses to antigens and PHA mitogen. This molecule is crucial for T-cell activation and signal transduction, as T cells cannot proliferate without it.
Area of Science:
- Immunology
- Cell Biology
Background:
- The T-lymphocyte receptor for antigen is a complex of surface glycoproteins.
- The OKT3 binding molecule is part of this complex and is hypothesized to be involved in signal transduction.
Purpose of the Study:
- To test if removing the OKT3 binding molecule eliminates T-cell immune responses.
- To investigate the role of the OKT3 binding molecule in T-cell activation and proliferation.
Main Methods:
- T cells from immune donors were enriched and surface molecules were cleared using OKT3 antibody and secondary antibodies.
- Regeneration of surface molecules was blocked by culturing cells with OKT3.
- Proliferative responses to antigens, alloantigens, and mitogens (PHA, A23187) were compared between capped, uncapped, and regenerated cells.
Main Results:
- T cells lacking the OKT3 binding molecule failed to proliferate in response to antigens and alloantigens.
- These capped cells also showed significantly reduced proliferation to PHA but responded to A23187.
- Cells with regenerated OKT3 binding molecules or untreated cells proliferated normally to antigens, alloantigens, and mitogens.
Conclusions:
- The OKT3 binding molecule is essential for T-cell proliferation induced by antigens, alloantigens, and PHA.
- This molecule likely conveys the transmembrane signal necessary for T-cell activation.
- PHA activation is impaired without the OKT3 binding molecule, possibly due to failed binding to its carbohydrate moiety.