SIGLEC-1 expression was significantly increased in SLE and MCTD patients when compared with SSc (8761.66 ± 8325.74 vs. 2097.94 ± 2134.39; p < 0.0001 and 6414.50 ± 1846.55 vs. 2097.94 ± 2134.39; p = 0.0003). Here, SIGLEC1 is linked to mixed connective tissue disease.