The Role of AVP on the Immunological Memory in the T‐Dependent Antigens Immune Response

Antigens can be classified as either T lymphocyte dependent (TLD) or as TL independent. In the immune response mediated by TLD antigens, T lymphocytes are essential to generate memory B lymphocytes (humoral acquired immunity). The role of arginine‐vasopressin (AVP) as an immunoregulatory hormone has been documented, however little is known about its role in the generation of long‐term immunological memory. Here we study the effects of low AVP serum levels (by neurointermediate pituitary lobectomy [NIL]), desmopressin (DP) (a synthetic AVP‐V2 receptors agonist) and conivaptan (CON) (an AVP‐V1a‐V2 receptors antagonist) on the immunological memory of rats immunized with sheep red blood cells (SRBC). Methods Male Wistar rats were divided in: 1) Control (Ctrl), 2) NIL, 3) Ctrl immunized (Imm), 4) NIL Imm, 5) Ctrl Imm+NIL, 6) NIL Imm+DP and 7) Ctrl Imm+CON groups. The group 5 was NIL at week 5 post primo‐immunization. In the remaining groups, neuro‐lobectomies were performed 3 weeks before primo‐immunization (week −3). SRBC immunizations (i.p) were at week 0 (primary) and week 8 (secondary). DP and CON treatments were administrated from weeks −1 to 1 and from 7 to 9 weeks. Serum hemagglutinin titers were assessed 1 week after each immunization. At sacrifice, spleen mononuclear cells (MNC) were isolated (ficoll gradient) and assessed. In thymus histological slides cortical and medullar MNC were counted (cells/mm 2 ) Results Hemagglutinin titers In the Ctrl‐Imm group, the secondary response was 9 times higher than the primary response. In the NIL Imm group no differences between primary and secondary responses were apparent. In the NIL Imm+DP group the secondary response was significantly increased, In the Ctrl Imm+CON group both primary and secondary responses were decreased. In the Ctrl Imm+NIL group (primo‐immunized at week 0 and NIL at week 5), a significant decrease in the secondary response was observed. Spleen MNC counts In the Ctrl Imm group a significant increased counts occurred whereas in NIL and NIL Imm groups no changes were observed. In Ctrl Imm+NIL group (NIL at week 5 post primo‐immunization), an increase in MNC was apparent. In NIL Imm+DP group no changes in MNC occurred, whereas in the Ctrl Imm+CON a non‐significant increase was observed. Cortical and Medullar thymic MNC counts In the Ctrl, Ctrl Imm and Ctrl Imm+DP no significant changes respect the Ctrl group were observed, whereas in NIL, NIL Imm and Ctrl Imm+NIL a significantly less counts were observed.Conclusions 1) AVP deficiency and CON decrease the TD antigens immune response including the long‐term immunological memory, 2) DP partially restores both: TD antigens humoral immune response and immunological memory, 3) It seems that thymus lymphocytes, more than spleen lymphocytes, plays the central role in the TD antigens immune response and on the maintenance of the long‐term immunological memory. Support or Funding Information Supported by UAA‐PIFF14‐1 and CONACYT‐221262 (AQS). México.