Low-level laser therapy reduces delayed hypersensitivity reaction to ovalbumin in Balb/C mice

The aim of this study was to evaluate the effect of low-level laser therapy (LLLT) in an experimental model of delayed hypersensitivity reaction (DTH). LLLT has been used clinically to treat numerous diseases and has been tested in different experimental models, but some of its effects have yet to be explained. We assessed the effects of LLLT on DTH to ovalbumin (OVA), a protein that has commonly been used as an antigen to sensitize laboratory animals. This experimental model is broadly used to assess the effects of substances that can potentially modulate the immune system and inflammatory reactions. Balb/C mice were randomly divided into four groups: (I) immunized, untreated, and challenged (n = 6); (II) not immunized, untreated, and challenged (n = 6); (III) immunized, treated with azathioprine (AZA), and challenged (n = 6); and (IV) immunized, treated with LLLT, and challenged (n = 6). Forty-eight hours after the challenge, the animals were submitted to a paw edema test and euthanized for histopathology analysis of their plantar pads. The results obtained in DTH units were as follows: Group I, 19.6 ± 8.9; Group II, 5.8 ± 2.6; Group III, 5.6 ± 2.5; and Group IV, 5.2 ± 2.6. DTH was less intense for the groups treated with AZA and laser compared with Group I (p < 0.05). We observed no statistical difference between the AZA- and LLLT-treated groups. The slides obtained from the footpad specimens showed that AZA and laser acted similarly on the normal pattern of DTH triggering. Our results suggest that treatment with LLLT has an immunomodulatory effect on DTH to OVA.