Immunomodulating activities of macroalgae

The immune requirements of broilers vary throughout the production cycle depending on the physiological status and are also influenced by external factors. This can include environmental stress such as temperature or stocking density, management stress such as vaccination programs, feed stress such as transitions or presence of toxins which can really impact the animals’ immune status. Sanitary pressure will also greatly impact immunity. This situation is aggravated if animals already present a low level of immunity.

New regulations aiming to ban antibiotics in broilers diets as a routine means of growth promotion has led to an intensive research effort to identify alternative bioactive compounds that are able to promote animal health. The modulation of the animal’s immune function is another approach leading to a higher resilience degree against external aggressors such as infectious agents. In-feed marine macroalgal polysaccharides have the potential to help animals face these daily challenges.

Specificities of macroalgal extracts

The cell wall of marine macroalgae is mainly composed of water-soluble sulphated polysaccharides which present a complex structure. The molecular weight and several structural specificities, including branched conformation, presence of several sugars and more particularly rare ones (xylose and rhamnose) and sulphation, confer to algal polysaccharides unique biological activities. Among others, modulation of the immune response and reinforcement of the gut barrier function are being investigated. Sulphated polysaccharides are specific from marine macroalgae (they are not found in terrestrial plants, nor fresh water microalgae or yeast cell walls) as the marine environment is the only one where sulphur chemical form can be integrated in the structure of organisms. Thanks to all these structural specificities, marine sulphated polysaccharides possess structural analogies with animal’s glycosaminoglycanes (GAG’s), like heparin. This explains their high degree of reactivity and specific biological activities when fed to animals.

Olmix Group innovative technology and marine bioactive ingredient extraction know-how lead to the development of an in-feed product, Algimun, which is based on the combination of two biologically active macroalgal extracts: MSP Immunity reinforces innate and adaptive immune responses; and MSP Barrier, which enhances the barrier function of the intestinal mucosa.

Assessing the immunomodulating traits

The immunomodulating activity of Olmix MSP Immunity (extracted from green macroalgae Ulva sp) was first evidenced on porcine intestinal epithelial cells in vitro. The solution induced the transcription of several immune mediators involved in the activation, recruitment and migration of macrophages and dendritic cells (professional antigen-presenting cells), as well as differentiation and recruitment of lymphocytes, and induction of anti-inflammatory properties, thus raising interest for its use as an immunomodulating agent. This activation was shown to derive from the activation of the pattern recognition receptors (PRR) Toll-like receptors (TLR) 4 and 2.

Further research has been conducted in poultry models in order to demonstrate the ability of the modulating agent to enhance innate and adaptive immune response of broilers through activation of heterophils and monocytes. Heterophils are functionally equivalent to mammalian neutrophils and are a critical component of innate immunity. Their activity can be evaluated by measuring the oxidative burst (release of reactive oxygen species (ROS) with bactericidal activity) and/or by conducting a degranulation assay, assessing the enzymatic activity of glucuronidase also able to degrade viruses and bacteria. Monocytes are important phagocytes in poultry, playing a critical role in both innate immunity (bactericidal activity via nitric oxide (NO) production) and initiation of the adaptive immune response (via their role as antigen-presenting cell).

Figure 1 – Nitric oxide release by monocytes with different concentrations of MSP Immunity during four consecutive days.

Data represents the mean ± SEM of 3 independent experiments with 25 chickens per group. Different letters with the same colour indicate statistically different values for the different doses at the same time with p < 0.05, different symbols with the same colour indicate statistically different values for the different doses at the same time with *p < 0.05, **p < 0.01, and ***p < 0.005 when values are statistically different for the same dose at different times. Extracted from Guriec et al.,2018.

Activation of monocytes and heterophils

The effect of MSP Immunity on birds’ monocytes and heterophils (purified from peripheral blood of 28 day-old broilers) was evaluated in vivo. 3 different concentrations of the solution (10, 25, 50mg/L) were given orally (per os) at day 0 (first day of the trial) for 24 hours and compared with the negative control. The experiments lasted 4 days in total. Results showed that MSP Immunity induced the activation of monocytes and heterophils. A dose and time response was observed for nitric oxide release by monocytes with a peak at day 1, swiftly declining, with values no longer statistically different from that of the negative control at day 3 (Figure 1).

Figure 2 – Glucuronidase activity by heterophils with different concentrations of MSP Immunity during four consecutive days.

Data represents the mean ± SEM of 3 independent experiments with 25 chickens per group. Different letters with the same colour indicate statistically different values for the different doses at the same time with p < 0.05, different symbols with the same colour indicate statistically different values for the different doses at the same time with *p < 0.05, **p < 0.01, and ***p < 0.005 when values are statistically different for the same dose at different times. Adapted from Guriec et al., 2018.

In parallel, the ability of the solution to induce glucuronidase activity in heterophils was also occurring in a time and dose-dependent manner (Figure 2). Additional in vitro experiments, using specific PRR inhibitors, showed that MSP immunity activates monocytes and heterophils through recognition by TLR2 and TLR4 confirming the results obtained by Berri et al. (2017) in a porcine model. Moreover, the study showed that the activation of monocytes and heterophils led to a transient increase of immune mediators transcription, including interleukin 1-β, interferon-α and interferon-γ. These cytokines are produced during innate immune responses and play an important role as activators of adaptive immune responses via the differentiation of Th1 cells that will determine cell-mediated immunity: antigen presentation activity of macrophages and induction of lymphocytes B to synthetize opsonizing antibodies.

Practical application

The study highlights the potent role of MSP Immunity to support the development of adaptive immune response in broilers. This bioactive compound can thus play an important role within the reduction of antibiotics in feed. Complementary trials in research centres or on the field have confirmed that when distributed continuously to broilers during starter and grower phases, it can accelerate the shift from innate to adaptive immunity (decreased heterophil to lymphocyte ratio), improving gut protection and technical performance.

References available on request

Author: María García Suárez, For Feed Product Specialist, Olmix Group