gluten
for good bread you need the right protein content in the milled grain flour. the basic chemical action of bread making is this: while the dough is proving, yeast and enzymes ferment and react to create carbon dioxide. in the oven the increasing temperature inside the loaf causes further gas production, until the yeast gets so hot that it dies, releasing the gas in bubbles which rise up through the dough. these bubbles are trapped in little pockets throughout the bread, leavening the bread as the gas tries to escape. gluten forms the "roof" of the pockets and traps the gas inside the loaf.
rye, barley and wheat all contain a number of proteins, including gluten. rye and barley are lower in protein which is why they're generally mixed with wheat flour for bread making. wheat (Triticum aestivum) is usually favoured for its predictable gluten levels. allowing for regional differences, winter wheat is generally "harder" at around 13-15% gluten, so good for strong bread (think of the big holes in a good ciabatta). warmer weather wheat is softer, around 4-9% gluten, producing a small, even crumb, like cake. durum wheat (Triticum durum) is even higher in protein and the hardness makes good pasta that doesn't absorb too much water during cooking. it's also milled into semolina, and some chewy, crusty Italian breads are made with durum flour or a mixture of durum and wheat flour.
Triticum spelta

and the gluten: spelt contains levels of gluten comparable to winter wheat, testing at roughly 10-26% and as high as 40% (this would generally be too strong for most types of bread). to be more specific about the protein, like wheat it contains both gliadin and glutenin, but in a different relationship than seen in wheat. some theories consider that gliadin is the cause of allergy in wheat-intolerant people, and some subjects show no reaction to spelt, but there seems to be lack of conclusive evidence at this stage.
so go ahead and make spelt bread without fear, I've tried it and it works, all is above board and beyond suspicion.
Stallknecht, G.F, K.M. Gilbertson, and J.E. Ranney. 1996. "Alternative Wheat Cereals as Food Grains: Einkorn, Emmer, Spelt, Kamut, and Triticale"
Field, C. 1985. The Italian Baker. New York. Harper & Row.
Bio-Distributors Biodynamic and organic wholesalers: Product history and cultivation
Symons, M. 2007. One Continuous Picnic. Melbourne. MUP.