Cross-reactivity between methylisothiazolinone, octylisothiazolinone and benzisothiazolinone using a modified local lymph node assay

Background:
In the light of the exceptionally high rates of contact allergy to the preservative methylisothiazolinone (MI), information about cross-reactivity between MI, octylisothiazolinone (OIT) and benzisothiazolinone (BIT) is needed. 

Objectives:
To study cross-reactivity between MI and OIT, and between MI and BIT. 

Methods:
Immune responses to MI, OIT and BIT were studied in vehicle and MI-sensitized female CBA mice by a modified local lymph node assay. The inflammatory response was measured by ear thickness, cell proliferation of CD4⁺ and CD8⁺ T cells, and CD19⁺ B cells in the auricular draining lymph nodes. 

Results:
MI induced significant, strong, concentration-dependent immune responses in the draining lymph nodes following a sensitization phase of three consecutive days. Groups of MI-sensitized mice were challenged on day 23 with 0·4% MI, 0·7% OIT and 1·9% BIT – concentrations corresponding to their individual EC3 values. No statistically significant difference in proliferation of CD4⁺ and CD8⁺ T cells was observed between mice challenged with MI compared with mice challenged with BIT and OIT.

Conclusions:
The data indicate cross-reactivity between MI, OIT and BIT, when the potency of the chemical was taken into account in choice of challenge concentration. This means that MI-sensitized individuals may react to OIT and BIT if exposed to sufficient concentrations.