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The first paper in this series reported that it was possible to reconstitute the response of low concentrations of mouse spleen lymphocytes to concanavalin A (Con A) by adding small numbers of peritoneal exudate cells (PEC) to the cultures. In this paper it is shown that the role of the PEC in this system can be partially replaced by conditioned medium (CM) prepared from PEC cultures or completely replaced by CM taken from lymphocytes cultured at optimal concentration. These CM were inactive unless fresh Con A was added to the assay cultures. Activity was present in CM which was incubated with lymphocytes or PEC for the shortest possible time but maximal activity was found after 24 hr of incubation. Activity was also found in CM prepared in the absence of Con A. Only in the case of lymphocytes cultured at optimal concentration for 24 hr was there substantially more activity in the CM thus prepared if Con A was present. PEC preparations depleted of T lymphocytes produced as much activity in CM as the untreated control. CM produced by PEC was less sensitive to heat treatment or to freezing and thawing than that produced by lymphocyte cultures. [ABSTRACT FROM AUTHOR]

With a long history of promoting pathological inflammation, eosinophils are now emerging as important regulatory cells. Yet, findings from controlled laboratory experiments so far lack translation to animals, including humans, in their natural environment. In order to appreciate the breadth of eosinophil phenotype under non‐laboratory, uncontrolled conditions, we exploit a free‐living population of the model organism Mus musculus domesticus. Eosinophils were present at significantly higher proportions in the spleen and bone marrow of wild mice compared with laboratory mice. Strikingly, the majority of eosinophils of wild mice exhibited a unique Ly6Ghi phenotype seldom described in laboratory literature. Ly6G expression correlated with activation status in spleen and bone marrow, but not peritoneal exudate cells, and is therefore likely not an activation marker per se. Intermediate Ly6G expression was transiently induced in a small proportion of eosinophils from C57BL/6 laboratory mice during acute infection with the whipworm Trichuris muris, but not during low‐dose chronic infection, which better represents parasite exposure in the wild. We conclude that the natural state of the eosinophil is not adequately reflected in the standard laboratory mouse, which compromises our attempts to dissect their functional relevance. Our findings emphasize the importance of studying the immune system in its natural context – alongside more mechanistic laboratory experiments – in order to capture the entirety of immune phenotypes and functions. [ABSTRACT FROM AUTHOR]

Leucocyte migration inhibitory (MI) activity was investigated in vitro in the delayed hypersensitivity reaction induced by intrapleural injection of PPD into FCA-sensitized guinea-pigs. During the initial reaction (6 h) two types of antigen-dependent MI activity were detected in serum and cell-free exudate. One was of high molecular weight and associated with immunoglobulin and the other was of low molecular weight and appeared to be related to so-called 'antigen-dependent MIF'. As the reaction progressed (i.e. 12-24 h), two types of antigendependent MI activity were revealed in exudate, but not in serum. One was high molecular weight and the other was low molecular weight and thought to be related to so-called 'antigen-independent MIF'. Similar experiments were performed on the reverse passive Arthus reaction in the pleural cavity of guinea-pigs. A high molecular weight MI activity was detected in 6-h cell-free exudate and was found to be antigen-independent. 'So-called MIF' was not found in this reaction. [ABSTRACT FROM AUTHOR]