Dear Doctor: What’s the connection between the novel coronavirus and the thymus gland? A friend of ours who is a doctor says it’s probably what keeps young kids from getting so sick. I’ve never even heard of the thymus. What does it have to do with coronavirus?

Dear Reader: From the earliest days of the novel coronavirus pandemic, the data revealed a puzzling disparity. Older adults were at increased risk of grave illness when infected with the virus, but children seemed to have a certain level of protection. And while it has since become clear that children can indeed become seriously ill if they become infected, they do so at far lower rates than adults. The reasons for this are still being investigated, but some researchers have recently suggested the role of the thymus gland as a possible factor.

If you place your finger at the notch at the top of your breast bone and draw a vertical line downward a few inches, you’ve traced the location of your thymus. It’s made up of two roughly triangular lobes, which sit behind the breastbone and between the lungs. The thymus has several functions, but perhaps its most important role is to help produce the cells that will become T-lymphocytes, or T-cells. (The "T" stands for thymus-derived.) These are white blood cells that protect the body from bacteria, fungi, viruses and other pathogens.

T-cells, which are the ninjas of the immune system, start out in the bone marrow as stem cells. The immature stem cells exit the marrow, move through the blood and enter a specific region of the thymus. There, they undergo a complex process that teaches them how to recognize a wide range of potentially dangerous and deadly invaders. As T-cells, their job is to circulate throughout the body and, when they encounter the molecular signature of the pathogen they’ve been trained to recognize, to attack. T-cells also activate other immune cells, produce proteins known as cytokines and have a role in regulating immune response.

The thymus is unique in that it reaches maturity in utero and is at its largest and most active in children. Starting at puberty, it gradually becomes less active, and the glandular tissue begins to shrink. This continues throughout a person’s life. By the time someone has reached their mid-60s, the thymus is largely inactive. By their mid-70s, the gland has been mostly replaced with fat. This decrease in thymus function is believed to be one of the reasons that, in their later years, older adults become more susceptible to disease and infection.

Emerging research into COVID-19 has shown a marked decrease in the number of T-cells in some gravely ill patients. Scientists are now asking whether age-related thymus decline, which means T-cells aren’t quickly replaced, may play a role in the severity of illness seen in older adults. The flip side of this is whether, due to their robust production of T-cells, children’s immune systems are able to stay one step ahead of the novel coronavirus. It’s only a working theory, but it shows promise, and research into how this may affect and inform treatment continues.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I’m 44 years old, and after wearing high heels to work for the last 20 years, I’ve lost flexibility in my feet. It also seems to be affecting my balance. Can you recommend foot exercises that can help?

Dear Reader: Considering the important work they do, our feet don’t get the attention they deserve. And yet, these complex systems of muscles, bones, tendons and ligaments form the base from which we balance, bear the full weight of our bodies and carry us through the thousands of steps in our daily lives.

One of the best things you can do for your feet is to give them a break from high heels, even just for a few days per week. Not only do high heels shift you forward and force your full weight onto the balls of your feet, they prevent you from properly using the muscles of your feet (and your legs) as you walk. Speaking of which, one of the best exercises for getting feet into shape is exactly that -- walking. Get a pair of supportive and flexible athletic shoes, and take a stroll. Be conscious of rolling through the foot, heel to toe, in a deliberate but natural motion. Don’t be surprised if this feels strange or even awkward at first. We tend to treat our feet as solid blocks rather than the intricate and articulated wonders that they actually are.

When it comes to a specific foot workout, exercises that take just a few minutes a day can make a difference.

-- Toe lift: Stand barefoot and, without straining, slowly and gently raise all 10 toes off the floor. Hold for a few seconds, then lower again. When you’re comfortable with this move, add some more repetitions, this time fanning your toes apart as you lift and lower them.

-- Heel lift: Engage your calf muscle and gradually raise your heel so that you balance on the ball of your foot. Hold for a few seconds, then gently lower again. If your ankles are strong, you can slowly and deliberately roll the ball of your foot from side to side and in a circular motion, which engages a range of muscles and -- bonus -- gives a nice massage. This exercise can be done either seated or standing.

-- Toe point: Extend your leg and, in a fluid motion that starts at the heel and rolls through the arch and down to the toes, gently extend your foot. Point your toes, hold for a few seconds, and then reverse the movement until you’re flexing your heel.

-- Toe dome: Standing barefoot, gently grip the floor with all five toes of each foot, as though you’re going to pick up a dollar bill. You’ll form a small dome when you’re doing this one right. Hold for a few seconds and then release.

Don’t try to do too much all at once. Work your way up to eight to 10 repetitions of each exercise. With just five minutes a day, you’ll soon regain strength and flexibility, and your feet will thank you.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I had a coronavirus test, and it was negative. Then I had the antibody test, and I was surprised when it came back positive because I hadn’t been sick. How do these coronavirus tests work? Are they accurate?

Dear Reader: There are two testing goals related to SARS-CoV-2, the coronavirus that causes COVID-19. One is to learn whether or not you are currently infected. The other is to see whether or not you have been infected in the past.

By far, the most common test being conducted at this time is for the coronavirus itself. This involves the use of a nasal swab, which is a long, thin stick with soft brushlike material on the tip. The swab is carefully inserted deep into the nose, to the passageway that connects to the back of the throat. (It’s uncomfortable, but not painful.) The goal is to gather a sample that includes cells and secretions from the back of the throat and from all along the length of the nose. Although there’s a less-invasive COVID-19 test that relies on just a throat swab, similar to the test used for strep throat, it’s not considered to be as accurate as the nasal swab. A newly developed saliva test, which requires just a sample of spit and returns a result within 30 minutes, has been submitted for regulatory review. Each of these tests look for genetic markers specific to SARS-CoV-2. Meanwhile, on July 3, the Centers for Disease Control and Prevention announced the development of a single test able to diagnose influenzas A and B as well as the novel coronavirus.

When you become sick with a virus, the immune system sends specialized proteins known as antibodies to mount an attack. Since antibodies are specific to the invader they are fighting, it’s often possible to identify when someone’s immune system has fought off a particular pathogen. It usually takes at least one week, and can take up to three weeks or longer, for the body to develop antibodies. Although it’s rare, despite being infected by a pathogen, some people don’t develop antibodies at all.

An antibody test is performed by screening a blood sample for specific markers of the antibody in question. Unfortunately, in the case of the novel coronavirus, the accuracy of these tests is in question. The CDC has found that up to half of antibody test results may be inaccurate, giving either a false positive or a false negative. A recent study examined 40 different types of antibody tests and found a wide disparity in their accuracy. The researchers suggested that until these tests are improved, people should not rely on the results.

As for having antibodies to SARS-CoV-2 despite not having been physically ill, that’s entirely possible. A hallmark of this virus is that some people, despite being infected, don’t develop symptoms. However, they can still pass along the virus, which is known as asymptomatic transmission. That’s why, in order to protect the people around us, it’s so important for each of us to wear a face covering in public, social distance and wash our hands.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)