From
http://www.digitalnaturopath.com/treat/T444777.html :
"While nuts do not contain histamine, they do contain histidine. Peanut, sesame, almond, pistachio, pine, and walnut have the highest levels of histidine among the nuts. Histidine, an amino acid, can be used by some gut bacteria to produce histamine. In other words, nuts can raise histamine levels indirectly. "
I can't vouch for the veracity of the site, but this was the most direct answer to the question I could find with a quick Google search.

If you're avoiding histamine foods, probably avoid nuts for a while and reintroduce one at a time to see the effect.