Autosomal recessive pituitary dwarf mice of the Snell-Bagg (SB)2 and Ames strains develop severe immunodeficiency which primarily affects the thymus-dependent system (1–5). The thymus undergoes a progressive involution which initially occurs as a depletion of thymocytes from the cortex accompanied by an increased number of lymphoid cells in the medulla. The next stage of thymus degeneration is a loss of lymphoid cellularity of the medulla, thereby causing complete atrophy (5).

In order to evaluate the immunologic reactivity of dwarf thymus and spleen cells, we have investigated their blastogenic response to phytohemagglutinin (PHA) and their ability to induce a graft-vs-host (GVH) reaction in immature F1 hybrid mice. Both tests determine the immunocompetence of thymus-dependent lymphoid cells.

Four-week-old dwarf and normal SB mice of both sexes were sacrificed by cervical dislocation. Their spleens and thymuses were removed and suspensions of each organ were prepared in cold Eagle's minimal essential medium (MEM) (Grand Island Biological Co., Grand Island, N. Y.).

1

Supported by grants from The Research Corporation, the American Cancer Society (Milwaukee Division) and PHS General Research Grant 5 SOL FR-5434.

2

Abbreviations used in this paper: SB, Snell-Bagg mice; PHA, phytohemagglutinin; GVH, graft vs host; MEM, Eagle's minimum essential medium.

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