Leukocyte ultrastructure of yellow pond turtles and Chinese box turtles

Yellow pond turtles had irregularly rounded heterophils with a generally smooth cytoplasmic membrane, which sometimes exhibited small, finger-like pseudopodia. The eccentrically located nucleus was pleomorphic, with moderate amount of peripheral heterochromatin. The cytoplasm was packed with numerous large, irregularly spindle-shaped (even elongated) and electron-dense

granules. One or more small, round and strongly electron-dense cores were frequently seen within the cytoplasmic granules. Free ribosomes and polyribosomes were dispersed within the cytoplasm.

Mitochondria were seen in small numbers, and vacuoles were also found; while endoplasmic reticulum was difficult to find.

Heterophils of the Chinese box turtles also had a generally smooth cytoplasmic membrane with few small pseudopodia. The eccentrically located nucleus was irregularly round to pleomorphic, with moderate amount of peripherally or centrally clumped heterochromatin. The cytoplasm was packed with primarily large, oval-shaped and moderately electron-dense granules (type I granules).

As in the yellow pond turtles, these granules were also frequently found with one or more small, rounded and strongly electron-dense cores. A second population of granules (type II granules) were also seen, which were fewer in number, smaller in size, round to elliptical in shape, and

significantly less electron-dense. Free ribosomes and polyribosomes were dispersed within the cytoplasm. Other membranous organelles such as mitochondria and endoplasmic reticulum were not commonly found, while vacuoles were clearly present.

Figure 20. Representative heterophil ultrastructure in yellow pond turtles and Chinese box turtles H: heterochromatin; U: euchromatin; V: vacuoles; c: core; I: type I granules; II: type II granules A: irregularly spindle-shaped and electron-dense granules, yellow pond turtles; B: the cytoplasm was packed with primarily large, oval-shaped granules with one or more strongly electron-dense cores, Chinese box turtles; C: close up details of the cytoplasmic granules, one or more strongly electron-dense cores were frequently seen, yellow pond turtles; D: close up details of the

cytoplasmic granules, a second population of granules (type II granules) were also seen, which were significantly less electron-dense, Chinese box turtles

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Eosinophils

Yellow pond turtles and Chinese box turtles had similar eosinophils ultrastructure. These cells were rounded with some finger-like pseudopodia. The N/C ratio was higher than that of

heterophils, and the large nucleus was irregularly round to indented, with abundant, peripherally and centrally aggregated heterochromatin. The cytoplasm was packed with numerous evenly sized, rounded granules with variable electron density (generally homogenously electron-dense). No cores or crystalline structure were identified within the granules, but vacuoles were frequently presented.

Free ribosomes and polyribosomes were dispersed within the cytoplasm, few mitochondria and vesicles were seen, but endoplasmic reticulum was difficult to find.

Figure 21. Representative eosinophil ultrastructure in yellow pond turtles and Chinese box turtles H: heterochromatin; U: euchromatin; P: pseudopodia; V: vacuoles; M: mitochondria

A: indented nucleus and evenly sized granules, yellow pond turtles; B: an irregularly rounded nucleus, cores or crystalline structure were not seen within the granules, but vacuoles were frequently presented, Chinese box turtles; C: close up details of the cytoplasmic granules, yellow pond turtles; D: indented nucleus and a few mitochondria were seen, Chinese box turtles

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Basophils

Yellow pond turtles and Chinese box turtles had similar basophils ultrastructure. These cells were rounded with a smooth cellular membrane, but occasionally few finger-like pseudopodia was present. The N/C ratio was high, and the large nucleus was irregularly round to pleomorphic, with abundant heterochromatin. The cytoplasm was packed with a highly heterogenous population of rounded to pleomorphic granules of varying size. Although identically basophilic under light microscope, it was fascinating to see the diversity of these granules on an ultra-microscopic level.

Many of them had a finely stippled content (type I granules), while a fewer but very conspicuous group of granules exhibited delicate patterns (sometimes termed as “honeycomb-like” or “reticular”

in literature) of unique kinds and different electron density (type II granules). These structures were identified as microtubules. The third group of cytoplasmic granules appeared irregularly round, relatively homogenous and electron-dense, while vacuoles were sometimes presented (type III granules). However, with uranyl acetate and lead citrate double staining, one or more crystalline inclusions were clearly seen within many of the type III granules. The crystalline structures were homogenously electron-dense, polygonal in shape, giving some type III granules an angular

appearance. Yellow pond turtles seemed to have dominant type I granules and less, smaller type III granules comparing to Chinese box turtles, but type II granules were rarest in both species. Other cytoplasmic organelles were not prominent in basophils of these species. Free ribosomes and

polyribosomes were dispersed within the cytoplasm, short segments of rough endoplasmic reticulum were occasionally seen, while other membranous organelles were difficult to find.

Figure 22. Representative basophil ultrastructure in yellow pond turtles and Chinese box turtles H: heterochromatin; U: euchromatin; V: vacuoles; I: type I granules; II: type II granules; III: type III granules; cs: crystalline structure

A: type I granules have finely stippled content, yellow pond turtles; B: type II granules have

honeycomb-like pattern, Chinese box turtles; C&D: crystalline inclusions were seen within many of the type III granules stained with uranyl acetate and lead citrate, Chinese box turtles

H

Lymphocytes

Lymphocytes were similar between yellow pond turtles and Chinese box turtles. These cells were round to elliptical in shape, with an irregular cellular membrane. The large, rounded nucleus took up most of the cellular space, and contained abundant amount of peripherally and centrally clumped heterochromatin. Free ribosomes and polyribosomes were dispersed within the scarce cytoplasm. Membranous organelles were scant in small lymphocytes, while multiple mitochondria, rough endoplasmic reticulum and small vesicles were clearly seen in large lymphocytes.

Figure 23. Representative lymphocyte ultrastructure in yellow pond turtles and Chinese box turtles H: heterochromatin; U: euchromatin; M: mitochondria; R: rough endoplasmic reticulum (RER); V:

vesicles

A: scant cytoplasm and membranous organelles in a small lymphocyte; B: abundant amount of clumped chromatin, multiple mitochondria, rough endoplasmic reticulum and small vesicles in a large lymphocyte, stained with uranyl acetate and lead citrate

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Monocytes

Monocytes were similar between yellow pond turtles and Chinese box turtles. These cells were irregularly round in shape, with a lower N/C ratio. The nucleus was irregularly round to indented, containing scant to variable amount of peripherally and centrally clumped

heterochromatin. The abundant cytoplasm was rich in membranous organelles. Numerous mitochondria, endoplasmic reticulum, vesicles of various size, small number of small, rounded, electron-dense granules, free ribosomes and polyribosomes were easily seen.

Figure 24. Representative monocyte ultrastructure in yellow pond turtles and Chinese box turtles H: heterochromatin; U: euchromatin; M: mitochondria; R: rough endoplasmic reticulum (RER); V:

vesicles

A: the indented nucleus contained mainly euchromatin, note the abundant cytoplasmic membranous organelles; B: abundant cytoplasmic membranous organelles

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