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It's easy to find general lists of immune systems: innate/adaptive, complement, phagocytes, B/T cells, and so on. Annoyingly, they are very skimpy on quantitative information regarding the speed of these reactions and that matters a lot.

I'm wondering how long after for example bacteria entering the body, do immune systems kick into action? I'm guessing the complement, clotting, and local phagocytes are the fastest but I could not find actual times required.

I found speeds for some immune systems but not for most. This recent recent study on the immune reaction against SARS-CoV2 has a rough time course with dendritic cells early and antibodies from activated B cells in weeks. This more detailed time course, also for Covid, shows the IgM peak at around 2 weeks ("The majority of patients appeared to have seroconverted by day 14").

Ok, but what about all the other processes? How fast can an innate immune cell hone in via chemotaxis, how fast are T killer cells on the scene upon viral infection, how fast is the complement or clotting cascade really, how does antibody production vary in speed between triggers and individuals? I hope you can point me towards any data that might shed light on this. I appreciate any leads.

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    $\begingroup$ As a possible lead: hit-and-run viruses, such as those related common cold, give up before the the adaptive immune system kicks in. This is how they avoid forming immunity in the hosts. And this is about a week time. $\endgroup$
    – Roger V.
    Commented Sep 3, 2021 at 15:47
  • $\begingroup$ Don't forget allergic reactions. $\endgroup$
    – DKNguyen
    Commented Sep 3, 2021 at 23:28
  • $\begingroup$ Thanks, Roger. That's very interesting. @DK: I guess immune overreactions = allergies often come in after the real defense work is done, don't they? $\endgroup$
    – SeanJ
    Commented Sep 4, 2021 at 7:28
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    $\begingroup$ I just point that out because your post was talking in terms of weeks, whereas allergic reactions take minutes $\endgroup$
    – DKNguyen
    Commented Sep 4, 2021 at 18:38

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Although it's focusing on mechanical injuries, Time Course of Immune Response and Immunomodulation During Normal and Delayed Healing of Musculoskeletal Wounds provides a number of time points for specific immune responses along with references. That should get you started.

This article is looking specifically at musculoskeletal injury situations rather than infections, and suggests that both the types of cells/responses involved and their timing can vary in other situations or infections. For the injury situations, they summarize:

Such injuries are associated with local inflammation and typically heal in the following order of events: inflammatory phase [0–7 days post-injury (dpi)]; regeneration phase (4–14 dpi); and remodeling and repair phase (14–>28 dpi).

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  • $\begingroup$ Answers shouldn't entirely depend on outside resources. You certainly don't need to recapitulate the whole reference, but can you include enough content so your answer would stand alone? $\endgroup$
    – Bryan Krause ♦
    Commented Sep 4, 2021 at 13:01
  • $\begingroup$ I see your point, but in this case the OP seems to be asking for so much detail that a partial recap or summary would be insufficient. The article is a review, so is already digested/summarized. I'll try to add some more to the answer. $\endgroup$
    – Armand
    Commented Sep 4, 2021 at 15:43

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