Clustering of early arthritis patient sera based upon microarray surface plasmon resonance imaging data. Microarray surface plasmon resonance imaging data for 374 early arthritis patient sera were subjected to cluster analysis using Cluster 3.0 software. The results were used to generate a heat map, with the results for the individual peptides given in rows (peptide numbers indicated on the right) and those for the patients given in columns. (A) through (L) On the basis of the dendrograms, 12 autoantibodies against citrullinated protein profiles were defined. Below the heat map, the anti-cyclic citrullinated peptide 2 (CCP2) reactivity is shown: anti-CCP2-positive is shown in different shades of brown and orange, and anti-CCP2-negative is shown in blue. Fib: fibrinogen; FN: fibronectin; Pep. Lib.: peptide library; MNDA: myeloid cell nuclear differentiation antigen; Vim: vimentin.