Mechanisms and selective expression of immunological tolerance
THE CONTEXT
The source describes proposed mechanisms of tolerance, differences between lymphocyte responses, and selective loss of an immune response.
Proposed mechanisms
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The mechanism of tolerance is not clear. Elimination of helper T cells, which prevents B cell activation, is described as a likely central mechanism.
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An afferent block interferes with antigen access to immunocompetent cells.
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An efferent block involves neutralisation or destruction of synthesised antibody.
Lymphocyte sensitivity and dose
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T lymphocytes are more susceptible to tolerance induction than B lymphocytes.
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In general, high antigen doses induce B cell tolerance, whereas repeated minute antigen doses induce T cell tolerance.
Split tolerance
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Tolerance to humoral and cellular immunity is usually induced simultaneously.
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Split tolerance occurs when unresponsiveness develops for one parameter of the immune response while another remains responsive.
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In guinea pigs, injecting tuberculoprotein before BCG immunisation can inhibit delayed hypersensitivity to tuberculin without affecting circulating antibody production.