Question

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.

Answer 1

The innate immune system responds almost immediately to pathogens, while the adaptive immune system takes longer, typically mounting a full response in 1-2 weeks. Memory cells from prior exposures result in a much faster response upon re-exposure. The specifics of these timings can vary with the nature of the pathogen and individual immune system differences.

Step-by-step explanation:

The timing of immune responses to pathogens varies depending on whether the pathogen is new to the body or one that has previously infected the individual. When bacteria or viruses enter the body, the innate immune system kicks in almost immediately, with mechanisms like the complement system and phagocytes reacting rapidly. The inflammatory response and chemotaxis of innate immune cells can occur within minutes to hours.

By contrast, the adaptive immune system takes more time to respond. Initial responses, such as the activation and proliferation of T cells, occur within days, but the full adaptive response, including the production of specific antibodies by B cells, generally takes 1-2 weeks. After about 10 days from the primary exposure, levels of IgM antibodies rise, marking the end of the lag period. Specific antibody production, such as IgG, then peaks about three weeks post exposure. In subsequent infections by the same pathogen, memory cells can mount a rapid response within hours to a few days, providing quicker protection.

Adaptive immunity involves T cells and B cells, with T cells differentiating into helper T cells or cytotoxic T lymphocytes (CTLs) and B cells producing antibodies. Memory cells persist after the primary exposure and provide a faster response upon re-exposure. Overall, the speed of these responses varies depending on the infection and individual factors.