CD4 and red-green color blindness: Furthermore, there are public (i.e., expressed in the majority of HLA-DP2-expressing CBD patients) beryllium-responsive TCRβ variable region (TRBV) 5.1+ TCRs expressed on CD4+ T cells derived from the BAL of CBD patients, and the frequency of these public beryllium-responsive TCRs inversely correlate with loss of lung function, suggesting that these public T cells are pathogenic in nature (75).