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I'm wondering if only humans, or only mammals have antibodies and immune system. Obviously humans and dogs have (we vaccinate both) and in my head makes sense since we're so genetically similar to all mammals that we all have antibodies. Do all synapsids, or even amniotes have antibodies as part of their immune system? Do plants have antibodies or insects?

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Apparently, cartilagenous fishes are the oldest extant clade that have the true immunoglobulins (antibodies) and the T-cell receptor (Schluter et al., 1997). All extant gnathostomes, incuding cartilagenous fishes, produce antibodies.

However other animals (invertebrates) and even plants have proteins that belong to the immunoglobulin superfamily (to which the classical immunoglobulins/antibodies also belong). Members of this superfamily are structurally related; they are not necessarily involved in immune responses. Hemolin is one immunoglobulin superfamily protein in insects, that is involved in immune function, but not exactly like vertebrate antibodies.

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  • $\begingroup$ In the animal kingdom adaptive immunity is present in all Gnathostomes. $\endgroup$
    – Tyto alba
    Oct 25, 2016 at 11:22
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    $\begingroup$ Agnathostomata (hagfish and lampreys) also have an immune system that is somewhat adaptive, although in many cases it isn't structurally related to the Gnathostome "adaptive immunity". For example, they have molecules that are analogous to antibodies, including a diversity-generating mechanism, but that are not structurally related to them. See for example Dual nature of the adaptive immune system in lampreys $\endgroup$
    – iayork
    Oct 25, 2016 at 12:36
  • $\begingroup$ @iayork.. I read that too but I as far as I have read they don't produce true antibodies (i.e. immunoglobulins). $\endgroup$
    – WYSIWYG
    Oct 25, 2016 at 13:36
  • $\begingroup$ @SanjuktaGhosh Yeah I forgot to explicitly state that explicitly but note that adaptive immunity does not really require antibody production as iayork has mentioned. $\endgroup$
    – WYSIWYG
    Oct 25, 2016 at 13:43
  • $\begingroup$ Definitely not true antibodies (they're structural more like TLRs, as I recall, though I don't recall if they're evolutionarily linked or not) but with surprisingly analogous aspects to them. Lamprey and hagfish immunity is really fascinating, since they share some aspects with Gnathostomes but also have gone in completely different directions in other ways $\endgroup$
    – iayork
    Oct 25, 2016 at 14:10

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