Immune suppression by ALS, irradiation and homologous antibody
THE CONTEXT
These interventions affect different components of immunity, and their effects depend on the target cells, timing or specificity of the intervention.
ALS effects and limitations
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ALS acts primarily against T lymphocytes and therefore specifically affects cell-mediated immunity.
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Humoral responses to thymus-independent antigens remain unaffected and may even increase.
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ALS acts against circulating lymphocytes, not cells in lymphoid organs.
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Because ALS is a foreign protein, repeated administration reduces its effect and may cause serum sickness or other hypersensitivity reactions.
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Monoclonal antibodies against specific lymphocyte membrane antigens have been prepared.
Whole body irradiation
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Sub-lethal whole body irradiation suppresses antibody responses.
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An antigenic stimulus given 24 hours after irradiation produces no antibody response.
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Giving antigen 2–3 days before irradiation enhances the antibody response.
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The primary immune response is more radiosensitive than the secondary response.
Suppression by homologous antibody
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Passive administration of homologous antibody can specifically suppress the humoral response to its antigen, apparently through a feedback mechanism.
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The primary response is more susceptible to this inhibition than the secondary response.
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The administered antibody may bind antigen and prevent its availability to immunocompetent cells.
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This effect is used to prevent Rh sensitisation in Rh-negative women carrying an Rh-positive fetus by administering anti-Rh globulin immediately after delivery, within 72 hours.