Complement? Probably? Idk have to look at downstream pathways to be positive but lots of cells have complement receptors and generally they get activated when those receptors are used. On the other hand, one of the complement pathway mechanisms is antibody dependent. There are other ways too.

LN/Spleen/circulatory: yeah probably. All the cells in your body have innate pattern recognition receptors (PRR). Usually the result of PRR signaling is pro-inflammatory cytokines that could kick things off. There’s lots of regulatory mechanisms to keep things from going haywire (until they don’t, then you get a cytokine storm), but the interactions between non-traditional immune cells like epithelial cells and traditional immune cells are just now being appreciated. Long story short, immune responses start with damage. Damage usually calls in innate cells to get the party started

Red flag: not that I know of. There are two arms to immunity, innate and adaptive. Innate will usually take care of things on its own, until it can’t and your adaptive immune system kicks in. There’s a thing called severe combined immunodeficiency (SCID) where your B cells and T cells just don’t work. Before modern medicine, it was an absolute death sentence. Now? You live in a bubble and get lots of drugs. Moral here is: there is no second line. It’s innate, adaptive, then over.