Gamma-linolenic acid is a weak Leukotriene B4 (LTB4) receptor antagonist.

Gamma-linolenic acid (GLA), an omega-6 fatty acid, is an essential fatty acid necessary for human health. You have to get them through food. Along with omega-3 fatty acids, omega-6 fatty acids play a crucial role in brain function, and normal growth and development. Omega-6 fatty acids, also known as polyunsaturated fatty acids (PUFAs), have been involved in stimulating skin and hair growth, maintaining bone health, regulating metabolism, and maintaining the reproductive system. Leukotriene B4 is a pro-inflammatory mediator involved in inducing recruitment and activation of neutrophils, monocytes and eosinophils, stimulating the production of a number of proinflammatory cytokines and mediators, indicating its ability to augment and prolong tissue inflammation. Elevated levels of leukotriene B4 have been identified in some inflammatory diseases and levels are related to disease activity in some of these [2].

Gamma-linolenic acid weakly antagonized LTB4 receptor activity, inhibiting [3H]-LTB4 binding to porcine neutrophil membranes with a Ki of 1 μM. GLA produced 53% inhibition at a 1 mg/kg dose in an in vivo model of LTB4-induced bronchoconstriction [1]. In promyelocytic HL60 cells, GLA are DNA safe (non-genotoxic) and antimutagenic, confirming its antioxidant capacity. GLA exhibited cytotoxic activity with an IC50 of 0.087 mM. GLA significantly decreased the life span of D. melanogaster [3]. Gamma -linolenic acid was effective and without side-effects for the treatment of patients with atopic dermatitis, distal diabetic polyneuropathy [4,5].

References:
[1] Yagaloff K A, Franco L, Simko B, et al.  Essential fatty acids are antagonists of the leukotriene B4 receptor[J]. Prostaglandins, leukotrienes and essential fatty acids, 1995, 52(5): 293-297.
[2] Crooks S W, Stockley R A.  Leukotriene B4[J]. The international journal of biochemistry & cell biology, 1998, 30(2): 173-178.
[3] Tasset-Cuevas I, Fernández-Bedmar Z, Lozano-Baena M D, et al.  Protective effect of borage seed oil and gamma linolenic acid on DNA: in vivo and in vitro studies[J]. PloS one, 2013, 8(2): e56986.
[4] Jamal G A, Carmichael H.  The Effect of γ‐Linolenic Acid on Human Diabetic Peripheral Neuropathy: A Double‐blind Placebo‐controlled Trial[J]. Diabetic Medicine, 1990, 7(4): 319-323.
[5] Andreassi M, Forleo P, Dilohjo A, et al.  Efficacy of γ-linolenic acid in the treatment of patients with atopic dermatitis[J]. Journal of International Medical Research, 1997, 25(5): 266-274.