Immune System Fortification With Snake Fruit

Overview

Have you ever heard of a fruit called snake fruit, or perhaps its alternate name, salak? Well, this nutritious fruit has numerous health benefits and a unique flavour and texture, making it hard to resist. 

Alongside its many benefits, snake fruit plays a role in fortifying the immune system by enhancing different cells and elements involved in the immune response against pathogens.

What is snake fruit?

Snake fruit (Salacca zalacca), alternately known as salak, is a tropical fruit commonly found in Southeast Asian countries, especially Indonesia. It is characterised by its fig-like appearance and a brown, scaly shell enveloping lobes of firm flesh with a seed embedded in the centre of each lobe. It has a complex flavour profile – sweet and tangy with a hint of acidity, a mixture of flavours between pineapple, banana and apple. 

Salak is a great source of a variety of nutrients, including vitamin C, dietary fibres and phosphorus, which is why it is commonly associated with a wide range of benefits including:

• Fortification of the immune system
• Regulation of blood glucose level
• Increase in energy level
• Improvement of cardiovascular health 
• Enhancement of memory 
• Promotion of digestion and bowel movement 

Introduction to the immune system

The immune system is the major contributor to the body's defence against invading pathogens, which are organisms that bring about diseases to the host, such as bacteria, viruses and fungi. It comprises numerous proteins, cells and organs, which all contribute to the system's three essential functions:

• Immunological recognition – the ability to distinguish between foreign and self¹
• Immune effector function – the ability to deal with infection and eliminate it without harming the body¹
• Immunological memory – the ability to improve the effectiveness of the immune response upon reencounter with the pathogen²

The immune system can be categorised into two parts, innate and adaptive, each with unique immune cells, activation pathways and effector functions. 

Innate immune response

The innate immune response acts as the early respondant when a pathogen initially infects the body. The immune cells involved include macrophages, neutrophils, eosinophils, mast cells, natural killer cells and dendritic cells. They each play distinct roles in detecting, communicating and destroying the pathogen.³ These cells are quick to act and are distributed throughout the body to allow thorough coverage of potential invasions. 

Adaptive immune response

The adaptive immune response is the delayed element and requires activation from the dendritic cells. It involves T cell lymphocytes, which play a role in regulation, activation and killing, and B cell lymphocytes, which produce antibodies and memory cells.⁴ The adaptive immune cells also enhance the innate immune response in clearing the infection. 

Despite their differences in the pathways and mechanisms, the innate and adaptive responses function collaboratively to destroy the pathogens and protect the body from harm effectively. 

How is the immune system fortified and why is it important?

One of the main benefits of snake fruit is the ability to strengthen the immune system. The fruit comprises a variety of molecules and compounds, each playing a specific role in the immune system. 

Polyphenols

Polyphenols are abundant in snake fruits. They have a significant role in the immune response in intestinal mucous and have antitumour properties.⁵ The mucosal layer is the outermost layer for the defence against pathogens in the gut and polyphenol increases the production of the eosinophils and T cells in response to the invasion in this layer. Eosinophils release granules which kill pathogens, whereas T cells not only have pathogen-destroying activity but also help with the enhancement of both the innate and adaptive systems.^6,7 

As for its role in antitumour growth, polyphenol enhances the activities of immune cells, such as natural killer cells, which release destructive granules to kill tumour cells and inhibit cells, such as some macrophages, which play a role in assisting the proliferation of cancer cells.⁸ By regulating the different immune cells, polyphenols can contain the tumour cells and prevent them from suppressing and weakening the immune system. 

Dietary fibre

Salek also contains a high content of dietary fibre, which plays a role in increasing mucosal immunoglobulin production and the amount of Peyer's patches (lymphatic tissue in the intestine).⁹ Dietary fibres play a factor in stimulating the activation of B cells, which can produce antibodies that protect the body from any pathogens on the mucosal surfaces. These immunoglobulins can bind to the pathogens and carry out immunological functions.¹⁰ 

On the other hand, Peyer's patches are involved in the surveillance of the intestinal environment and the detection of foreign pathogens. They contain an array of immune cells, such as T cells, B cells and dendritic cells, thus an increase in the numbers improves the circulation of these immune cells to the sites of infection.¹¹ 

Vitamin C 

Vitamin C is abundant in snake fruits and plays a role in assisting the innate immune system. It enhances the immunological functions of neutrophils during an infectious response.¹² Vitamin C promotes the movement of neutrophils to the site of infection by improving the sensitivity of these immune cells to chemoattractant stimuli.¹³ 

It also improves the microbiocidal effect of neutrophils by stimulating the increased production of superoxide radicals, which play an essential role in killing pathogens.¹⁴ Vitamin C also induces neutrophil apoptosis and reduces the necrosis of these immune cells.¹⁵ Apoptosis and necrosis both result in cell death, but apoptosis is a more controlled process, whereas necrosis is less regulated and leads to an uncontrolled release of the cellular contents. When neutrophils die from apoptosis rather than necrosis, the membrane of the immune cell is maintained, which prevents the toxic granules within the cell from being released to the surroundings, minimising the damage dealt to unaffected cells. 

Cytokines

A study showed that snake fruit peel extract (SFPE), obtained by dissolving the freeze-dried skin of the fruit with water and then purifying it, has a role in fortifying the immune system of mice. It played a role in increasing the phagocytic activity and production and expression of cytokines (proteins to regulate inflammation).¹⁶ Enhancing the phagocytosis of the pathogens allows for increased engulfing, leading to more antigen presentation for the activation of immune cells and the microbicidal killing of these pathogens.¹⁷

 Moreover, SFPE has been shown to increase the amount of cytokines like tumour necrosis factor-alpha (TNF-ɑ) and interleukin-6 (IL-6). TNF-ɑ is involved in recruiting immune cells to the site of infection, increasing vascular permeability to allow passage of these cells and other related components of the immune system and promoting the effector function of other immune cells.¹⁸ IL-6, on the other hand, stimulates the growth and differentiation of B and T cells, significantly strengthening the adaptive immune response.¹⁹ 

An important matter to note is that since the study utilised mouse cells as the target due to the difficulty of obtaining human macrophages, more research would be needed to investigate its effectiveness in the human body. However, based on the success of a study carried out by Pantic et al., it can be considered that similar effects can be applied to human macrophages.²⁴ 

Incorporation of snake fruit into meals  

Despite the immunological benefits the skin of the snake fruit contains, it is not eaten and peeled off before consumption. The flesh of the fruit can be used in a variety of methods:

• Eaten raw directly 
• Used along with other fruits and vegetables, such as a salad
• Cooked into dishes, such as curries and stir-fries
• Preserved for a long period through candying and pickling 

It is important to note that the seed is not edible for most varieties of snake fruit and must be taken care of when preparing the flesh. 

Overconsumption of snake fruit

Due to its low calories and fat content, it might be easy to overlook the potential consequences of excessively eating snake fruit. 

• Due to the fibrous content of this fruit, overconsumption would lead to periodic intervals of diarrhoea, along with bloating, cramping and buildup of intestinal gas²⁰ 
• Snake fruit is also rich in vitamin C and can benefit the human body in many ways. However, due to the acidic nature of the vitamin, they are metabolised into oxalate when excreted in urine and increase the risk of forming kidney stones when consumed over the recommended amount^21,22 
• Although salak has a low glycemic index, it is important to be wary of the fruit's sugar content. The glycemic index only indicates the speed at which the food is absorbed, it does not address the rise in blood glucose level. If an excessive amount of sugar is consumed, it can lead to diseases like obesity, type 2 diabetes and cardiovascular diseases²³ 

Summary 

Yes, snake fruit does strengthen the body's immune system, but excessive eating would have an impact on human health. These nutritious fruits bring about a considerable amount of benefits and can be consumed in many ways. However, it is vital to be mindful of the level of consumption to maximise its benefits for the body.