Hl. Lenzi et al., COELOM-ASSOCIATED LYMPHOMYELOID TISSUE (MILKY SPOTS) - SITE OF LYMPHOID AND MYELOMONOCYTIC CELL GENERATION, Brazilian journal of medical and biological research, 29(1), 1996, pp. 19-24
Pleural and peritoneal milky spots (MS) are small morphofunctional str
uctures representing subsidiary foci of coelom-associated lymphomyeloi
d tissue (CALT). In this paper we studied the cellular composition of
CALT in normal and Schistosoma mansoni-infected mice. In the healthy m
ouse, CALT is mainly composed of IgM (+) B cells and presents lower nu
mbers of CD23 and CD45R (B220) B2 lymphocytes. When activated by the i
nfection, it may show pronounced lymphocytosis, plasmocytogenesis (IgM
>IgG>IgA>IgG2a>IgG1) and myelomonocytosis. The lymphocytes were mainly
of the B1 type (double positive CD5/IgM), with smaller number of T ce
lls(TCR alpha beta(+),TCR gamma delta(+), CD3(+) and CD5(+)) and conve
ntional B2 cells (B220(+),CD23(+)). The myeloid compartment was compos
ed of immature and mature cells of monocyte/macrophage, eosinophil, ne
utrophil and megakaryocytic lineages, especially in the omental milky
spots. CALT is also a favorable microenvironment for LFA-1 (+) mast ce
lls. Thus, CALT appears to be a mixed lymphoid organ, with secondary a
nd/or primary lymphoid organ functions, being an important site of B1
cell generation, plasma cell maturation and extramedullar hematopoiesi
s. CALT operates as an interface between blood and lymphatic circulati
on and coelomic cavities, because locally or externally produced cells
have easy and ready access to the pleural and peritoneal cavities. Fu
rthermore, MS cells can escape into blood and lymphatic vessels, provi
ding lymphocytes to other lymphoid organs and to the mucosa-associated
lymphoid tissue.