The most common and most likely answer to this crossword clue is the 5 letter word THYMI
I've seen this crossword clue in Independent
T
H
Y
M
I
More clues leading to the result THYMI
Buddy explains!

The straight part
We know that "glands" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case glands = thymi.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does THYMI mean?
THYMI noun- A ductless gland, consisting mainly of lymphatic tissue, located behind the top of the breastbone. It is most active during puberty, after which it shrinks in size. It plays an important role in the development of the immune system and produces lymphocytes.