Prevention of infection by a temperate phage of a lysogen as mediated by a prophage of the same immunity type.
Also described as homoimmunity and superinfection immunity. Phages differ in terms of their immunity types where phages of the same immunity type said to be homoimmune to each other; by contrast, phages of different immunity types are said to be heteroimmune. Note that immunity is an intracellular process that follows both phage adsorption and phage-genome translocation and is based on prophage repressor action. See also immunity region and intemperate.
Immunity should not be confused with exclusion, that is, superinfection exclusion, which is a means by which phages prevent the uptake of phage nucleic acid into already phage-infected bacteria. Immunity, by contrast, functions against nucleic acid that is already found within the infected bacterium's cytoplasm. This is the definition from Adams (1959, InterScience, p. 440): "Resistance to infection that does not result from failure of the phage to adsorb and inject, characteristically associated with the lysogenic state." From Gill and Young (2012), p. 402: "Bacterial insensitivity to a phage caused by lysogeny of the cell by the same or related phage; this term only relates to temperate phages."
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