Abstract
It is well known that functionally different two major subpopulations of lymphocytes are present-T lymphocytes (Thymus derived) and B lymphocytes (Bone marrow derived)-. Although they can be distinguished by specific surface receptors, surface antigen markers and electrophorectically different morbility, they are not morphologically distinguishable by light and electron microscopy. Recently it has been shown that the human T cells are smooth in surface, whereas B cells are villous by scanning electron microscopy (SEM). But Scott has reported by SEM used immunospecific latex markers that there was no distinct morphological difference between mouse T and B lymphocytes.
In the present study, we have observed lymphocytes of athymic nude mice (nu/nu) and nu/+ mice using freeze fracturing in an attempt to demonstrate the morphological difference between them.
Nude mice and nu/+ mice, ages 6-8 weeks were killed with ether and their inguinal lymphnodes were removed. One portion of each removed tissue was placed in 10% formalin and stained with hematoxylin and eosin for light microscopy. A second portion was immersed in 40% glycerol containing the cacodylate buffer and processed for freeze fracture.
The inguinal lymphnode of the nude mouse is relatively larger in size than that of nu/+ mouse. Although the small lymphocytes are present in the cortex, the expanded paracortical area completely lacks small lymphocytes. The lymphoid follicles are poorly developed and rather small in size.
Most of the lymphocytes of the nude mice are 4-8 μ in diameter, have a few short projections and only a few are villous.
In fracturing the membrane is often split along the middle of the lipid bilayer. Globular particles measuring 60 to 160 Å in diameter are present within the interior of the membrane exposed by freeze cleaving. The number of these particles per unit area (μ2) is 235-512(average density of 307) on the inner fracture face.
Most of the particles are present singly and only 2% of the nude mouse lymphocytes shows small aggregates of granule, while the lymphocytes of the thymus and the lymphnodes of the nu/+ mice show a higher percentage of particle aggregation by incubating in glycerol before freezing. Recently it has been suggested that the intramembranous particles may consist of protein and interact with a hydrophobic portion of glycoprotein or represent a receptor site. We agree with Mandel who suggested that the aggregates of the IP is one of the features of T-derived lymphocytes.
A relatively thick rim of the cytoplasm contain fairly well developed organelles in the nude mice. The nucleus is prominent and smooth in outline with scattered nuclear pores. The average pore density of the nude mouse is 19.2/10 μ2 and is fairly lower than that of thymus and lymphnodes of nu/+ mice.
The density of the intramembranous particles and the nuclear pores of the nuclear envelope may show the degree of the nuclear metabolic activity and/or the degree of the cell maturity. Therefore we suggest that the lymphocytes of the nude mouse may have less metabolic activity, but further studies are needed.
