Differential Activities of Rabbit Bone Marrow Suppressor Cells

Abstract

A population of nonadherent Fcγ-receptor-bearing (FcγR⁺) suppressor cells in normal rabbit bone marrow (BM) which inhibited the constitutive proliferation of other BM cells has been previously described. Suppression was by blocking the release of a soluble growth-promoting factor. In the present report, it was found that the FcγR⁺ BM suppressor cells, which were suppressive to background proliferation, were not suppressive to lymphocyte activation by immune complexes (IC). Adherent BM cells showed suppressive activity toward IC stimulation, but none toward constitutive BM proliferation. IC-induced proliferation was enhanced by the soluble growth factor, but only in the absence of adherent cells. Adherent cells did not affect growth factor enhancement of constitutive proliferation, suggesting that different cell populations were affected. Depletion of the FcγR⁺ suppressor cells promoted growth of cells which subsequently developed FcγR⁺, increasing the possibility of interaction with IC, which also preferentially induced FcγR⁺ cells.

Inflammatory Changes in Bone Marrow Microenvironment Associated with Declining B Lymphopoiesis

“…One of these was adherent, and had macrophage-like morphology (61), similar to the suppressive cells that we found within the CD11b + myeloid fraction, potentially MDSCs. The other suppressor cells were described as non-adherent, FcRγ+, complement receptor negative, and were thought to be suppressor lymphocytes (61, 62). If so, based on current knowledge, these cells could be Treg cells, IL-10-producing Bregs (63), or inflammatory TNF-producing aged B cells (ABCs) (27).…”

“…If so, based on current knowledge, these cells could be Treg cells, IL-10-producing Bregs (63), or inflammatory TNF-producing aged B cells (ABCs) (27). We suggest that the 2 nd “suppressor cell” of Soderberg (61) is likely an ABC because these cells are known to inhibit B cell development and to be increased in BM of aged mice (27). MDCSs are also increased in aged BM (4) and if they produce IL-1, we expect this would synergize with TNF (28) to skew the BM toward myelopoiesis instead of lymphopoiesis.…”

Lung histopathological findings in COVID-19 disease – a systematic review

“…Included studies underwent quality check and risk of bias assessment. This qualitative analysis was performed according Murad’s quality checklist of case series and case report [ 17 ]. As reported, the scale consists of four parameters, to evaluate the a) patient selection; b) exposure ascertainment; c) causality and d) reporting.…”

Bone marrow fat and the decline of B lymphopoiesis in rabbits

“…Several years ago, Soderberg and colleagues (1984a, 1984b) identified two types of suppressor cells in rabbit BM, one of which may be similar to the recently-identified MDSCs. The first suppressive cell, an adherent macrophage-like population inhibited proliferation and activation of BM cells after immune complex stimulation.…”

“…One such, as-yet-undescribed factor induces the accumulation of IL-1-secreting MDSCs, which inhibits B lymphopoiesis (Kennedy and Knight, 2015). It will be interesting to determine if these MDSCs are similar to the macrophage-like suppressor cells found in rabbit BM by Soderberg (1984a), or whether another inhibitory cell contributes to the decline of B lymphopoiesis. Other important issues include understanding what initiates changes in the BM microenvironment and increased fat deposition; are MSCs affected by changes in the microenvironment, and to what extent do they contribute to the changes; can the microenvironment, especially the large amount of fat in adult BM be reversed, and if so, how will this affect hematopoiesis.…”