136 The Lymphocyte and Lymphocytic Tissue 



MECHANISMS OF LYMPHOCYTOSIS 



The following discussion of the mechanism of lymphocytosis is necessarily 

 brief because Chapters 1 and 5 deal directly or indirectly with mechanisms. 



Much that has been written on this subject is conjecture and does not 

 bear repeating. One of the fundamental laws of hematology is that the 

 number of cells occurring at any given time in the peripheral blood are 

 determined by the net effect of three processes: (1) the number of cells 

 produced in the responsible hemopoietic tissue, (2) the rate at which these 

 cells are released into the blood stream, and (3) their life span. If we attempt 

 to apply critically these criteria to an elucidation of the mechanism by which 

 lymphocytosis is produced, Ave soon find that we are floundering in a sea 

 of ignorance or controversy. 



For example, there can be little argument with the concept that lympho- 

 cytes are produced exclusively in lymphoid tissues. In addition to lymph 

 nodes, lymphoid tissue is widely scattered throughout the body in organs 

 such as the spleen, bone marrow, and gastrointestinal tract, and also in a 

 diffuse fashion in many other locations. Certainly one route by which 

 lymphocytes enter the blood stream is by way of the thoracic duct, but it is 

 easier to imagine lymphocytes from the gastrointestinal tract finding their 

 way into the thoracic duct and the venous blood than to picture the migra- 

 tion of lymphcocytes through a series of lymph nodes into the collecting 

 lymphatic vessels and then into the blood stream. It is probable that 

 lvmphocytes also enter capillaries directly without being transported by 

 the thoracic duct, but I know of no data to indicate whether or not this is 

 true and, if so, what the relative proportion is of lymphocytes entering the 

 blood stream by various routes. We obviously do not know the rate at which 

 these cells are released from the lymphopoietic tissues. At one time it 

 was thought that a count of the number of lymphocytes per cubic millimeter 

 of lymph in the thoracic duct gave a measure of the total number of lympho- 

 cytes entering the blood stream and that from this estimates of their life 

 span could be made. More recent work indicates that one needs to revise 

 radically old concepts about the life span of lymphocytes, their biologic 

 behavior, and their fate; also the manner by which they enter and leave 

 the blood stream, where they go, and how long they last at each location. 

 At this time we must be satisfied to ask questions for which we do not know 

 the answers. 



