Micronodular thymoma with lymphoid stroma: an immunohistochemical study of the distribution of Langerhans cells and mature dendritic cells in six patients.
OBJECTIVE
Micronodular thymoma with lymphoid stroma (MNT) is an uncommon variant of thymoma, characterized by multiple small nodules consisting of type A thymoma-like cells, which are separated by abundant B lymphocytes. The aim of the study was to elucidate the pathogenesis of the stromal lymphoid hyperplasia, which is currently unclear.


RESULTS
We retrieved six cases of MNT, and immunohistochemically examined the number and distribution of Langerhans cells (LCs) and mature dendritic cells (DCs), and compared them with those in type A and type AB thymomas. Many LCs were present within the small tumour nests, but LCs were rarely seen in the stroma (75.5/HPF versus 6.1/HPF, P < 0.0001). In contrast, mature DCs were present mainly in the surrounding stroma rather than within the tumour nodules (63.5/HPF versus 6.0/HPF, P < 0.0001), forming clusters with mature T lymphocytes adjacent to lymphoid follicles. In large nodules, as well as in type A and type AB thymomas, a few scattered LCs and DCs were identified. All patients were still alive and well.


CONCLUSIONS
Our results suggest that LCs take up tumour antigens and migrate to the stroma, where they mature and form clusters with T lymphocytes to activate them, resulting in lymphoid follicle formation. The favourable clinical behaviour may be attributable to the immune response induced by LCs.
Department of Thoracic Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan.
Yoshinori
Y
Ishikawa
Hisashi
H
Tateyama
Megumi
M
Yoshida
Koji
K
Takami
Haruhisa
H
Matsuguma
Tetsuo
T
Taniguchi
Noriyasu
N
Usami
Koji
K
Kawaguchi
Takayuki
T
Fukui
Futoshi
F
Ishiguro
Shota
S
Nakamura
Kohei
K
Yokoi
D000368:Aged; D001402:B-Lymphocytes / Q000473:pathology; D003713:Dendritic Cells / Q000473:pathology*; D005260:Female; D018858:Germinal Center / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D007801:Langerhans Cells / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D013945:Thymoma / Q000276:immunology / Q000473:pathology*; D013953:Thymus Neoplasms / Q000276:immunology / Q000473:pathology*
Langerhans cell; dendritic cell; immunohistochemistry; micronodular thymoma