THE CONTEXT
The passage contrasts agents that enhance immune responses with agents used to inhibit immunity, including in transplantation.
Freund’s complete adjuvant and muramyl dipeptide
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Freund’s complete adjuvant consists of incomplete adjuvant with a suspension of killed tubercle bacilli.
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It increases humoral responses and induces a high degree of cellular immunity, including delayed hypersensitivity.
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Its production of a local granuloma makes it unsuitable for human use.
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The adjuvant effect of tubercle bacilli is attributed to the water-soluble peptide muramyl dipeptide (MDP). MDP induces a good antibody response without causing granuloma.
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MDP also stimulates cell-mediated immunity when given in mineral oil or as liposomes. The passage describes MDP derivatives as being developed for human use.
Other adjuvants
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The adjuvant effect of Gram-negative bacilli is attributed to their lipopolysaccharide fraction.
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Bordetella pertussis has an additional lymphocytosis-promoting factor acting on T and B cells and acts as an adjuvant for diphtheria and tetanus toxoids in the triple vaccine.
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Aluminium hydroxide and aluminium phosphate are listed as adjuvants commonly used with human vaccines.
Immunosuppression and radiomimetic drugs
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Immunosuppressive agents inhibit immune responses and are useful when graft rejection must be prevented.
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Radiomimetic drugs have actions resembling those of X-rays and generally belong to the alkylating-agent class; cyclophosphamide and nitrogen mustard are examples.
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The passage describes cyclophosphamide given for three days after antigen exposure as completely suppressing the antibody response in humans; administration before the antigen is much less effective.
Corticosteroids
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Corticosteroids deplete lymphocytes from blood and lymphoid organs.
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They stabilise cell and lysosomal membranes, inhibiting histamine release and the inflammatory response.
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Therapeutic doses have little effect on antibody formation in humans but inhibit the induction and manifestations of delayed hypersensitivity.