How biological differences between men and women alter immune responses and affect women's health
Birmingham (The Conversation): Most people will have heard the term "man flu", which refers to men's perceived tendency to exaggerate the severity of a cold or a similar minor ailment.
What most people may not know is that, generally speaking, women mount stronger immune responses to infections than men.
Men are more susceptible to infections from, for example, HIV, hepatitis B, and Plasmodium falciparum (the parasite responsible for malaria).
They can also have more severe symptoms, with evidence showing they're more likely to be admitted to hospital when infected with hepatitis B, tuberculosis, and Campylobacter jejuni (a bacteria that causes gastroenteritis), among others.
While this may be positive for women in some respects, it also means women are at greater risk of developing chronic diseases driven by the immune system, known as immune-mediated inflammatory diseases.
Here we will explore how biological factors influence immune differences between the sexes and how this affects women's health.
While we acknowledge that both sex and gender may affect immune responses, this article will focus on biological sex rather than gender.
Battle of the sexes
There are differences between the sexes at every stage of the immune response, from the number of immune cells, to their degree of activation (how ready they are to respond to a challenge), and beyond.
However, the story is more complicated than that. Our immune system evolves throughout our lives, learning from past experiences, but also responding to the physiological challenges of getting older.
As a result, sex differences in the immune system can be seen from birth through puberty into adulthood and old age.
Why do these differences occur? The first part of answering this question involves the X chromosome. Females have two X chromosomes, while males have one X and one Y chromosome. The X chromosome contains the largest number of immune-related genes.
The X chromosome also has around 118 genes from a gene family that are able to stop the expression of other genes, or change how proteins are made, including those required for immunity.
These gene-protein regulators are known as microRNA, and there are only two microRNA genes on the Y chromosome.
The X chromosome has more genes overall (around 900) than the Y chromosome (around 55), so female cells have evolved to switch off one of their X chromosomes. This is not like turning off a light switch, but more like using a dimmer.
Around 15-25 per cent of genes on the silenced X chromosome are expressed at any given moment in any given cell.
This means female cells can often express more immune-related genes and gene-protein regulators than males. This generally means a faster clearance of pathogens in females than males.
Second, men and women have varying levels of different sex hormones.
Progesterone and testosterone are broadly considered to limit immune responses.
While both hormones are produced by males and females, progesterone is found at higher concentrations in non-menopausal women than men, and testosterone is much higher in men than women.
The role of oestrogen, one of the main female sex hormones, is more complicated. Although generally oestrogen enhances immune responses, its levels vary during the menstrual cycle, are high in pregnancy and low after menopause.
Due in part to these genetic and hormonal factors, pregnancy and the years following are associated with heightened immune responses to external challenges such as infection.
This has been regarded as an evolutionary feature, protecting women and their unborn children during pregnancy and enhancing the mother's survival throughout the child-rearing years, ultimately ensuring the survival of the population.
We also see this pattern in other species including insects, lizards, birds and mammals.
What does this all mean?
With women's heightened immune responses to infections comes an increased risk of certain diseases and prolonged immune responses after infections.
An estimated 75-80 per cent of all immune-mediated inflammatory diseases occur in females.
Diseases more common in women include multiple sclerosis, rheumatoid arthritis, lupus, Sjogren's syndrome, and thyroid disorders such as Graves disease.
In these diseases, the immune system is continuously fighting against what it sees as a foreign agent.
However, often this perceived threat is not a foreign agent, but cells or tissues from the host. This leads to tissue damage, pain and immobility.
Women are also prone to chronic inflammation following infection.
For example, after infections with Epstein Barr virus or Lyme disease, they may go on to develop chronic fatigue syndrome, another condition that affects more women than men.
This is one possible explanation for the heightened risk among pre-menopausal women of developing long COVID following infection with SARS-CoV-2, the virus that causes COVID.
Research has also revealed the presence of auto-antibodies (antibodies that attack the host) in patients with long COVID, suggesting it might be an autoimmune disease.
As women are more susceptible to autoimmune conditions, this could potentially explain the sex bias seen.
However, the exact causes of long COVID, and the reason women may be at greater risk, are yet to be defined.
This paints a bleak picture, but it's not all bad news. Women typically mount better vaccine responses to several common infections (for example, influenza, measles, mumps, rubella, hepatitis A and B), producing higher antibody levels than men.
One study showed that women vaccinated with half a dose of flu vaccine produced the same amount of antibodies compared to men vaccinated with a full dose.
However, these responses decline as women age, and particularly after menopause.
All of this shows it's vital to consider sex when designing studies examining the immune system and treating patients with immune-related diseases.
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China slaps a 34 pc tax on all US imports in retaliation for Trump's tariffs
Bangkok (AP): China announced Friday that it will impose a 34 per cent tax on all US imports next week, part of a flurry of retaliatory measures to US President Donald Trump's new tariffs that delivered the strongest response yet from Beijing to the American leader's trade war.
The tariffs taking effect Thursday match the rate that Trump this week ordered imposed on Chinese products flowing into the United States. In February and March, Trump slapped two rounds of 10 per cent tariffs on Chinese goods, citing allegations of Beijing's role in the fentanyl crisis.
The US stock market plunged Friday following China's retaliatory moves. They include more export controls on rare earth minerals, which are critical for various technologies, and a lawsuit at the World Trade Organization over what Trump has dubbed reciprocal tariffs.
China also suspended imports of sorghum, poultry and bonemeal from six US companies, added 27 firms to lists of companies facing trade restrictions, and launched an anti-monopoly investigation into DuPont China Group Co., a subsidiary of the multinational chemical giant.
Trump posted Friday on Truth Social: “CHINA PLAYED IT WRONG, THEY PANICKED - THE ONE THING THEY CANNOT AFFORD TO DO.”
Yet he also indicated he could still negotiate with China on the sale of TikTok even after Beijing pressed pause on a deal following the new tariffs. On Friday, he extended the deadline for the social media app to divest from its Chinese parent company, per a federal law, for another 75 days.
“We hope to continue working in Good Faith with China, who I understand are not very happy about our Reciprocal Tariffs,” Trump posted on his social media site. “We look forward to working with TikTok and China to close the Deal.”
China's response to tariffs grows tougher
Beijing's response is “notably less restrained” than during the recent two rounds of 10 per cent tariffs on Chinese goods, and that “likely reflects the Chinese leadership's diminished hopes for a trade deal with the US, at least in the short term,” wrote Gabriel Wildau, managing director of the consultancy Teneo.
He said Beijing's tough response could trigger further escalation, with no sign that Chinese President Xi Jinping and Trump might meet soon or get on the phone to ease the tensions.
If China's previous responses were scalpels, this time it drew a sword, said Craig Singleton, senior China fellow at the Foundation for Defense of Democracies, a Washington-based think tank.
“China's new tariffs stop short of full-blown trade war, but they mark a clear escalation — matching Trump blow-for-blow and signaling that Xi Jinping won't sit back under pressure,” Singleton said.
But the escalation also is squeezing out space for diplomacy, he warned.
“The longer this drags, the harder it becomes for either side to deescalate without losing face,” Singleton said.
What China's retaliatory measures look like
In Beijing, the Commerce Ministry said it would impose more export controls on rare earths — materials used in high-tech products such as computer chips and electric vehicle batteries. Included in the list was samarium and its compounds, which are used in aerospace manufacturing and the defense sector. Another element called gadolinium is used in MRI scans.
China's customs administration said it had suspended imports from two US poultry businesses after officials detected furazolidone, a drug banned in China, in shipments from those companies. It said it found high levels of mold in the sorghum and found salmonella in the bonemeal feeds from four other US companies.
The Chinese government said it also added 16 US companies to the export control list, subjecting them to an export ban of dual-use products. Among them are High Point Aerotechnologies, a defense tech company, and Universal Logistics Holding, a publicly traded transportation and logistics company.
An additional 11 US companies were added to the unreliable entity list, including the American drone makers Skydio and BRINC Drones, banning them from import and export activities as well as making new investments in China.
In announcing its WTO lawsuit, the Commerce Ministry said Trump's new tariffs move “seriously violates WTO rules, seriously damages the legitimate rights and interests of WTO members, and seriously undermines the rules-based multilateral trading system and international economic and trade order.”
The ministry called the tariffs “a typical unilateral bullying practice that endangers the stability of the global economic and trade order.”
Beijing's previous tariff moves
In February, in response to Trump's first 10 per cent tariff, China announced a 15 per cent tariff on imports of coal and liquefied natural gas products from the US It separately added a 10 per cent tariff on crude oil, agricultural machinery and large-engine cars.
A month later, Beijing responded to Trump's second round with additional tariffs of up to 15 per cent on imports of key US farm products, including chicken, pork, soy and beef. Experts then said Beijing exercised restraint, leaving room for negotiations with Washington.
By now, dozens of US companies are subject to controls on trade and investment, while many more Chinese companies face similar limits on dealings with US firms.
While friction on the trade front has been heating up, the two sides have maintained military dialogue.
US and Chinese military officials met this week for the first time Trump took office in January to share concerns about military safety on the seas. The talks held Wednesday and Thursday in Shanghai were aimed at minimizing the risk of trouble, both sides said.
