What is the morphological difference between Leydig cell in human and pig?

Question

The pig is only an example, just an animal. Leydig cells have protein inclusions (Reinke crystals) that are mostly made of crystallised lipofuscin. They are secretory inclusions i.e. cells formed in secreting cells.

An example of Leydig cell in pig's testicle:

My teacher told me that there is a difference in the existence of some cells between humans and animals. However, I cannot find such a difference. I have not been provided a slide of human Leydig cell so I have not been able to compare.

What is the morphological difference between Leydig cell in human and pig?

Answer 1

Perhaps what your teacher meant was not so much a difference in Leydig cell morphology, but in interstitial tissue morphology, ie. tissue which occupies the space in between seminiferous tubules. Leydig cells are its most interesting component, others being small blood vessels (a lot of them), nerves and connective tissue (mostly fibroblasts, mastocytes, lymphocytes and macrophages). In different species interstitial tissue looks differently, for example:

• Leydig cells form clumps around blood vessels, and are surrounded by fibroblasts (which makes them more difficult to isolate) in guinea pig, but not in mice or rat;
• in human a lot of interstitial tissue is extracellular matter, Leydig cells are not so frequent, but more active;
• and, last but not least, in pig, there is little extracelluar matter and a lot of Leydig cells that are very easily isolated (and produce large amounts of estrogen).

I found all this in some old lecture notes; I couldn't dig up any sensible reference, though.

Answer 2

I have studied all available (via University library) literature on the Leydig cells and I think your teacher might have this article summarizing the morphological studies on Leydig cells in different animal models in mind.

To put it straight, the most common animal models for studying Leydig cells are rats, mice and pigs.

The development of Leydig cells in rats was shown to be bi-phasic: development of the Leydig cell population in fetus and its degradation while transforming into the mature cells. It has been believed for quite long that this is also true for human Leydig cells. However, some studies performed on pigs and monkeys delivered an evidence for an additional phase of cell degradation sometimes between the fetal and neonatal development shifts. These data are summarized on the following Figure (taken from the referenced paper):

So, by comparing the Leydig cells of rats and humans from the same fetus age or shortly after the birth (neonatal time) you might see the degradation of Leydig cells -- they decrease in size and many of them eventually die -- compared to normal state of these cells in rats.