LL37 is a natural antibiotic, but is also a molecule with pleiotropic functions as well as an immune-modulator. LL37 is produced by epithelial cells and is present in neutrophils’ granules. LL37 alone, or in complex with DNA, can activate inflammatory pathways in psoriasis, systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). In this work, we describe the capacity of two recombinant monoclonal antibodies, RB139 and RB142, previously shown to specifically recognize LL37 in its citrullinated form (cit-LL37) by ELISA, to detect LL37 by immunofluorescence in human inflamed tissues derived from SLE and RA patients. Such antibodies represent previously unavailable tools to detect the presence, the citrullinated state and the exact localization of cit-LL37 in human tissues in health and disease.